227. _c.v._, caudal vesicle or bladder (small); _sec. c._, secondary

cavity caused by the growth forward of the hind-body; _t._, tail bearing six spines. (Stephens.)] [Illustration: FIG. 199.--Diagram of a cysticercus. _c.v._, caudal vesicle or bladder; _i._, invagination of wall of bladder. (Stephens.)] In the case of cysticerci a papilliform invagination forms, projecting into the interior of the bladder (fig. 201). The layer of cells forming the papilla becomes divided into two laminæ, the outer[279] of which forms a kind of investing membrane (receptaculum capitis) for the papilla. The head and suckers are now developed on the walls bounding the axial lumen of the papilla. The papilla eventually evaginates, so that the receptaculum capitis now forms the inner surface of the hollow head, which eventually becomes solid. [279] _I.e._, regarded from the interior or centre of the invagination. Our knowledge of the development of cysticerci in the wide sense of the word is limited almost exclusively to that of a few true “bladder worms” (cysticerci); in other cases we know either only the terminal stage, _i.e._, the complete larva, or, exceptionally, one of the intermediate stages, but we are not acquainted with a complete series; the description must therefore be incomplete. We know from feeding experiments that, after the introduction of mature proglottids or of the fully developed ova of _Tænia crassicollis_ (of the cat) into the stomach of mice, the oncospheres escape from the shell in the middle portion of the small intestine, and a few hours later penetrate into the intestinal wall by means of a boring movement; they have been found in this position twenty-seven to thirty hours after the infection. By means of this migration, for which purpose they employ their spines, they attain the blood-vessels of the intestine; indeed, already nine hours after the infection and later they are found in the blood of the portal vein, and in the course of the second day after infection they are found in the capillaries of the liver, which these larvæ do not leave. Leuckart, in experimental feeding of rabbits with oncospheres of _Tænia serrata_ (of the dog), found free oncospheres in the stomach of the experimental animal, but not in the intestine: however, he came across them again in the blood of the portal vein. The passage through the blood-vessels to the liver is the normal one for those species of _Tænia_ the eggs of which become larvae in mammals; even in those cases in which the oncospheres develop further in the omentum or in the abdominal cavity (_Cysticercus tenuicollis_, _C. pisiformis_), there are distinct changes observable in the liver that lead one to the conclusion that there has been a secondary migration out of the liver into the abdominal cavity. Indeed, one must not imagine that the young stages of the Cestodes are absolutely passive; once they have invaded an organ they travel actively, and leave distinct traces of their passage. In other cases the oncospheres leave the liver with the circulation, and are thus distributed further in the body; they may settle and develop in one or more organs or tissues. Many oncospheres may, by travelling through the intestinal wall, penetrate through it and attain the abdominal cavity direct; some, perhaps, pass also into the lymph stream. Where there are no blood and lymphatic vessels in the intestinal wall, as in insects, the oncospheres attain the body cavity or its organs direct; in short, they never remain in the intestinal lumen itself, and only rarely--as in _Hymenolepis murina_ of the rat--do they remain in the intestinal wall. When the infection has been intense, and the body is crowded with numerous oncospheres, acute feverish symptoms, are induced, to which the infected animals usually succumb (“acute cestode tuberculosis”); while in other cases the alterations in the organs attacked--as the liver in mice and the brain in sheep--may cause death. Sooner or later the oncospheres of tapeworms come to rest, and are first transformed into a bladder, which may be round or oval according to the species. The embryonal spines disappear sooner or later, or remain close together or spread over some part of the bladder wall (fig. 200). Their discovery by V. Stein in the bladder worm of the “meal worm” (the larva of a beetle, _Tenebrio molitor_) first led to the conclusion that bladder worms (cysticerci) actually originate from the oncospheres of _Tæniidæ_. [Illustration: FIG. 200.--Diagram of development of a cysticercus. 1, solid oncosphere with six spines; 2, bladder formed by liquefaction of contents; 3, invagination of bladder wall; 4, formation of rostellum (with hooklets) and suckers at the bottom of the invagination; 5, evagination of head; 6, complete evagination effected by pressure. (Stephens.)] The bladder may remain as a bladder, and then by proliferation the scolex forms on its wall (fig. 202), or it may divide into an anterior so-called “cystic” portion and a solid tail-like appendage of various lengths, on which the embryonal hooks are to be found, and this is particularly the case in those larval forms (cysticercoids), _e.g._, those of _Dipylidium caninum_, that develop in invertebrate animals, such as Arthropoda. As mentioned above one may regard the scolex as an individual that originates through proliferation of the wall of the parent cyst, mostly singly, but in those cysticerci that are termed cœnurus (fig. 201) many scolices occur, whereas in those called echinococcus the parent cyst originating from the oncosphere of _Tænia echinococcus_ (of the dog) first produces a number of daughter cysts, which in their turn form numerous scolices. Echinococcus-like conditions also occur in cysticercoids, as, for instance, in those peculiar to earthworms; and similar conditions prevail in a larval form known as _Staphylocystis_, found in the wood-louse (_Glomeris_). Thus it happens in these cases that finally _one_ tapeworm egg produces not _one_, but numerous tapeworms, for, under favourable conditions, each scolex can form a tapeworm. [Illustration: FIG. 201.--Section through a piece of a _Cœnurus cerebralis_, with four cephalic invaginations in different stages of development. At the bottom of the invaginations the rostellum, hooks and suckers develop. (From a wax model.)] [Illustration: FIG. 202.--Median section through a cysticercus, with developed scolex at the bottom of the invagination. (After Leuckart.)] The rudiment of the scolex appears as a hollow bud, the cephalic invagination usually directed towards the interior of the bladder cavity; on its invaginated surface arise the four suckers, and the rostellum with the hook apparatus is formed in its blind end; we thus get a Tænia head, but with the position of the parts reversed (fig. 201). In many cysticerci the head rises up from the base of the cephalic invagination and is then surrounded by the latter. A more or less elongated piece of neck also develops, and even proglottids may appear, as in _Cysticercus fasciolaris_ (the larva of _Tænia crassicollis_ of the cat) of the Muridæ, a process somewhat analogous to that of Ligula, etc. The period that elapses from the time of infection till the cysticercus is fully developed varies according to the species; the cysticercus of _Tænia saginata_ requires twenty-eight weeks, that of _T. marginata_ seven to eight weeks, that of _T. solium_ three to four months, and that of _T. echinococcus_ longer still. [Illustration: FIG. 203.--_Cysticercus pisiformis_ in an evaginated condition, with neck, fore-body and bladder, with excretory network in its wall. 18/1.] With one single exception (_Archigetes_) the larvæ do not become sexually mature in the organ where they have developed; they must enter the terminal host, a matter that is usually purely passive, the carriers of the larvæ or infected parts of them being usually devoured by other animals. In this manner, for instance, the larvæ (_Cysticercus fasciolaris_) found in mice and rats reach the intestine of cats; those of the hare and rabbit (_C. pisiformis_) reach the intestine of dogs; those of the pig (_C. cellulosæ_) are introduced into man; those of insects are swallowed by insectivorous birds; those of crustaceans are ingested by ducks and other water fowl; perhaps, also, the infection of herbivorous mammals is caused by their accidentally swallowing smaller creatures infected by larvæ. Indeed, the researches of Grassi and Rovelli have taught us that such an intermediate host is not always necessary; _Hymenolepis murina_ of rats and mice in its larval stage lives in the intestinal wall of these rodents, and as a larva it passes into the intestinal lumen and develops into a tapeworm in exactly the same way as the larvæ of other species that reach the intestine of the terminal host by means of an intermediate carrier. Probably this curtailed manner of transmission also occurs in many other species. In some cases the larvæ actively quit the body of the intermediate host, as in the case of _Ligula_ and _Schistocephalus_, which travel out of the body cavity of infected fish and reach the water, where they may be observed in hundreds in summer, at all events in some localities. The larval stage of _Calliobothrium_--wrongly termed _Scolex_--has been observed swimming free in the sea, and the scolices of _Rhynchobothrium_, without their mother cysts, have been observed free within the tissues of several marine animals. In any case there is almost always a change of hosts, even in the single-jointed Cestodes, for the larva of _Caryophyllæus_, which lives in fishes of the carp family, is found in limicoline Oligochætes, that of _Gyrocotyle_ (Chimæra) in shell-fish (Mactra), and different conditions can hardly be possible for _Amphilina_. _Archigetes_ alone becomes sexually mature in the larval stage, but the life-history of this creature is not well known, so that it is not impossible that the attainment of sexual maturity as a larva in invertebrates (Oligochætes) is perhaps abnormal, and somewhat analogous to the maturity of some encysted Trematodes. The METAMORPHOSIS OF THE LARVA into the tapeworm is rarely accomplished in a simple manner; the transformation, however, is not complex in the single-jointed Cestodes, nor in _Ligula_ and _Schistocephalus_; the latter is swallowed by birds (_Mergus_, _Anas_, etc.), produces eggs after only a few days, and very soon quits the intestine of its terminal host. In all other cases it is the scolex only which, by proliferating at its posterior extremity, forms the proglottids, after having invaded as a larva the intestine of a suitable host. The mother cysts, or what corresponds to them, die, are digested, absorbed, or perhaps even eliminated; on the contrary, segments found on the scolex during the larval stage, also in the case of _Cysticercus fasciolaris_, are retained. It is not certain whether the larvæ of _Dibothriocephalus_ lose any part. The time required by the scolex to complete the entire chain of proglottids does not depend only on the number it has to produce, for _Tænia echinococcus_, which, as a rule, only possesses three or four segments, takes quite as long a time for their growth (eleven to twelve weeks) as _T. solium_ with its numerous segments; _T. cœnurus_ is fully developed in three to four weeks, and the same holds good for _Dibothriocephalus latus_, which possesses many more segments than the above-mentioned Tænia of the dog. In a number of species it has been possible to determine fairly accurately the average daily growth; for instance, in _Dibothriocephalus latus_ the daily growth is 8 cm., in _Tænia saginata_ 7 cm., etc. The history of the development of the Cestodes demonstrates that persons and beasts harbouring larval tapeworms have become infected by having swallowed the oncospheres of the species of tapeworm to which they belong. In regard to _Hymenolepis murina_ alone, it is known that the introduction of the oncospheres into those species of animals which harbour the adult tapeworm leads to the formation of the latter after the development of a larval stage in the intestinal wall; nevertheless, only young animals (rats) are capable of infection, for a previous infection, or the presence of mature tapeworms in the intestine, appears to produce a kind of immunity. BIOLOGY. In their adult stage, the tapeworms inhabit almost exclusively the alimentary canal of vertebrate animals, with but few exceptions the small intestine, and a few species select definite parts of it. A small number of _Rhynchobothriidæ_ of marine fishes live apparently always in the stomach, while in rays and sharks the spiral intestine is their exclusive site. Bothriocephali generally attach themselves with their head on to the appendices of the pylorus of fishes; other species (_Hymenolepis diminuta_) occasionally fix their head in the ductus choledochus, and this is more frequent still in the tapeworms of the rock badger (_Hyrax_), which occasionally penetrate entirely into the biliary ducts. _Stilesia hepatica_, Wolffh., has so far only been found in the bile-ducts of its host (sheep and goat, East Africa). In the disease of sheep induced by Cestodes, the worms have been observed also in the pancreas. Specimens found in the large intestines were probably being evacuated. The Cestodes are looked upon as fairly inert creatures, this opinion having been formed by observing their condition in the cold cadavers of warm-blooded animals. Actually, however, they are exceedingly active, and accomplish local movements within the intestine, for they have been found in the ducts communicating with the bowel, or in the stomach, and may even make their way forward into the œsophagus. They also invade other abdominal organs through abnormal communications, or through any that may be temporarily open between the intestine and such organs; they thus reach the abdominal cavity or the urinary bladder, or they work their way through the peritoneum. They produce changes in the intestinal mucous membrane at the place of their attachment, the alterations varying in intensity according to the structure of the fixation organs. The mucous membrane is elevated in knob-like areas by the suckers; the epithelial cells become atrophied or may be entirely obliterated. _Dipylidium caninum_ bores into the openings of Lieberkühn’s glands with its rostellum, dilating the lumen to two or three times its normal size, while the suckers remain fixed between the basal parts of the cells. Species with powerful armatures penetrate deeper into the submucosa, and some that are not provided with exceptionally strong armatures, or are even unarmed, may be actually found with the scolex embedded in the muscles of the intestinal walls or even protruding beyond (_Tænia tetragona_, Mol., in fowls, etc.). Other species, again, even cause perforation of the walls of the intestine of their hosts. It is generally assumed that tapeworms, which almost without exception live in the gut of vertebrates, get their nutriment from the gut contents, which apparently they absorb through the whole body surface (cuticular trophopores). In favour of this view is the existence of fat drops in the proglottids, the identity in colour in certain forms between that of the fresh worm and the gut contents and the passage of certain substances derived from medicines (iron and mercury preparation) into the worms in the gut, etc. Whether the suckers are concerned in the absorption of nutriment and to what extent is still questionable. THE LENGTH OF LIFE OF THE ADULT TAPEWORM certainly varies; as a rule it appears to last only about a year; in other cases (_Ligula_) it averages only a few days, but we are likewise aware that certain species of Cestodes of man attain an age of several or many years (thirty-five). The natural death of Cestodes often appears to be brought about by alterations in the scolex, such as loss of the hooks, atrophy of the suckers and rostellum, finally the dropping off of the scolex; it is unknown whether a chain of segments deprived of its scolex then perishes or whether it first attains maturity. It has already been mentioned that in a few species the foremost proglottids are transformed into organs of fixation on the normal loss of the scolex. Abnormalities and malformations are encountered relatively frequently in the Cestodes--such as abnormally short or long segments; the so-called triangular tapeworms, which--if belonging to the _Tæniidæ_--always possess six suckers; often also club-shaped segments occur between normal ones, or there may be a defect in one segment or in the centre of a number following one another (fenestrated segments); bifurcated chains of segments have likewise been observed, as well as incomplete or complete union of the proglottids, abnormal increase of the genital pores, reversion of the genitalia. Besides the above-mentioned increase of the number of suckers on the scolex (in Tæniæ), there may be a decrease in the number; in other cases the crown of hooks may be absent, or abnormally shaped hooks may be formed. CLASSIFICATION OF THE CESTODA OF MAN. Order. *Pseudophyllidea*, Carus, 1863. Scolex without proboscis or rostellum. Head “stalk” absent. Scolex never with four, generally with two (or one terminal) bothria.[280] Vitellaria numerous. Uterine opening present. Genitalia do not atrophy when uterus is developed. In large majority of proglottids eggs (or, if formed, their contents) are at the same stage of development. [280] _Bothridia_ or “_phyllidia_” are _outgrowths_ from the scolex. They are concave and extremely mobile. By some authors the term “_phyllidium_” is used for the outgrowth, and the term “_bothridium_” is restricted to the muscular cup. _Bothria_, on the other hand, are grooves more or less wide, the musculature of which is only slightly developed and is not separated off internally from the parenchyma. _Acetabula_, or suckers in the usual sense, are hemispherical cups, without lips and with musculature separated internally from the parenchyma. Family. *Dibothriocephalidæ*, Lühe, 1902. Syn.: _Diphyllobothriidæ_, Lühe, 1910. Genitalia repeated in each proglottid (polyzootic Cestodes). Ventral and dorsal surfaces flat. Cirrus unarmed. Cirrus and vagina if non-marginal open on the same surface as the uterus. Uterus long, convoluted, often forming a “rosette,” never dilates into a uterine cavity. Eggs thick shelled, operculated, constantly being formed in mature proglottids. Sub-family. *Dibothriocephalinæ*, Lühe, 1899. Syn.: _Diphyllobothriinæ_, Lühe, 1910. Segmentation distinct. Scolex unarmed, elongated, sharply separated (generally by a neck) from the first proglottis. Cirrus and vagina open ventrally. Genital pores non-alternating. Vas deferens surrounded by a muscular bulb. Receptaculum seminis large, sharply separated from the spermatic duct. Order. *Cyclophyllidea*, v. Beneden. Four suckers always present. Uterine opening absent. Vitellarium single. Genitalia atrophy when uterus is fully developed. Family. *Dipylidiidæ*, Lühe, 1910. Rostellum if present armed. Suckers unarmed. Uterus breaks up into egg capsules. Paruterine organs absent. Family. *Hymenolepididæ*, Railliet and Henry, 1909. Segment always broader than long. Genitalia single. Longitudinal muscles in two layers. Genital pores unilateral. Testes one to four. Uterus persistent, sac-like. Eggs with three shells. Family. *Davaineidæ*, Fuhrmann, 1907. Rostellum cushion-shaped. Armed with numerous (sixty to several thousand) hammer-shaped hooks in two (rarely one) rows. Sub-family. *Davaineinæ*, Braun, 1900. Suckers armed. Uterus breaks up into egg capsules. Paruterine organs absent. Family. _Tæniidæ_, Ludwig, 1886. Suckers unarmed. Uterus with median longitudinal stem and lateral branches. Female genitalia at the hind end of the proglottis. Genital pore irregularly alternating. Testes numerous in front of female genitalia. Ovary with two lobes (wings). Vitellarium behind the ovary. Embryophore radially striated. THE CESTODES OF MAN. Most of the species to be mentioned live in man in their adult stage and occupy the small intestine; man is the definite host of these parasites, but is not the specific host for all the species; some of these species, as well as others (of mammals), may occur in man also in the larval stage. Family. *Dibothriocephalidæ.* Sub-family. *Dibothriocephalinæ.* Genus. *Dibothriocephalus*, Lühe, 1899. Syn.: _Diphyllobothrium_, Cobbold, 1858; _Bothriocephalus_, p. p. Rud., 1819; _Dibothrius_, p. p. Rud., 1819; _Dibothrium_, p. p. Dies., 1850. Scolex egg-shaped; dorsal and ventral bothria elongated, moderately strong, cutting rather deeply into the head; genitalia single in each proglottis; papillæ in the vicinity of the genital atrium; the testes and vitellaria are in the lateral fields, the former in the medullary layer, the latter in the cortical layer on both surfaces, and occasionally extending to the median line; the ovary ventral, the shell gland dorsal. The uterus is in the central field, taking a zigzag course, and frequently forms a rosette. *Dibothriocephalus latus*, L., 1748. Syn.: _Tænia lata_, L., 1748; _Tænia vulgaris_, L., 1748; _Tænia grisea_, Pallas, 1796; _Tænia membranacea_, Pall., 1781; _Tænia tenella_, Pall., 1781; _Tænia dentata_, Batsch, 1786; _Bothriocephalus latus_, Bremser, 1819; _Dibothrium latum_, Dies., 1850; _Bothriocephalus cristatus_, Davaine, 1874[281]; _Bothriocephalus balticus_, Kchnmstr., 1855; _Bothriocephalus latissimus_, Bugn., 1886. [281] Until recently this worm, which was understood to belong to a separate species, was proved on examination by R. Blanchard (“Mai. Par.,” 1896), to be _Dibothriocephalus latus_. Compare also Galli-Valerio, in _Centralbl. f. Bakt., Path. und Infektionskr._, 1900 (1), xxvii, p. 308. Length 2 to 9 m. or more; colour yellowish-grey; after lying in water the lateral areas become brownish and the uterine rosette brown. The head is almond-shaped, 2 to 3 mm. in length, the dorso-ventral axis is longer than the transverse diameter; the head, therefore, generally lying flat, conceals the suctorial grooves at the borders; these suckers are deep and have sharp edges (fig. 205). The neck varies in length according to the degree of contraction and is very thin; there are 3,000 to 4,200 proglottids and there may be more; their breadth is usually greater than their length, but in the posterior third of the body they are almost square, and the very oldest are not uncommonly longer than they are broad. There are numerous testes situated dorsally in the medullary layer of the lateral fields; the vas deferens (fig. 192) passes dorsally in transverse loops in the central field anteriorly and forms a seminal vesicle before its entry into the large cirrus pouch. The orifice of the vagina is close behind the orifice of the cirrus; the former passes almost straight along the median line posteriorly, and widens into a receptaculum seminis shortly before its junction with the oviduct; the ovary is bilobed, in shape like the wings of a butterfly, ventrally in the medullary layer; the shell glands lie in the posterior recess of the ovary; the uterus, forming numerous transverse convolutions, passes ventral to the vas deferens forwards. Eggs (fig. 207) large, with brownish shells and small lids, 68 µ to 71 µ by 45 µ; the ovarian cell, which is already, as a rule, in process of segmentation, is surrounded by numerous large yolk cells; the proglottids nearest the posterior extremity are frequently eggless. [Illustration: FIG. 204.--Various chains of segments of _Dibothriocephalus latus_, showing the central uterine rosette. (Natural size.)] [Illustration: FIG. 205.--Transverse section of the head of _Dibothriocephalus latus_. 30/1.] [Illustration: FIG. 206.--Fairly mature proglottis of _Dibothriocephalus latus_. The vitellaria are at the sides; the uterus, filled with eggs, is in the middle, also the vagina (the dark stripe passing almost straight from the front to the back), and the vas deferens (almost hidden by the uterus). Above in the centre is the cirrus sac, and below the shell gland and ovary are seen. 15/1. (From a stained preparation.)] The eggs, which are deposited in the intestine and evacuated with the fæces, hatch in water after a fortnight or more; the embryonal integument (embryophore) of the oncosphere is provided with cilia; after bursting open the lid of the egg the oncosphere in its embryophore (fig. 207) reaches the water and swims slowly about; often it slips out of its ciliated embryophore, sinks to the bottom and is capable of a creeping motion; sooner or later it dies in the water. The manner and means of its invasion of an intermediate host are still unknown; yet we are aware that the larval stage (plerocercoid, fig. 208), which resembles the scolex and may reach a length of 30 mm., lives in the intestine, in the intestinal wall, in the liver, spleen, genital glands and muscular system (fig. 209) of various fresh-water fish, the pike (_Esox lucius_), the miller’s thumb (_Lota vulgaris_), the perch (_Perea fluviatilis_), _Salmo umbla_, _Trutta vulgaris_, _Tr. lacustris_, _Thymallis vulgaris_ (grayling), _Coregonus lavaretus_, _C. albula_ (in Europe) and _Onchorhynchus perryi_ (in Japan). The transmission of the plerocercoids from these fish to the dog, cat and man (Braun, Parona, Grassi and Ferrara, Grassi and Rovelli, Ijima, Zschokke, Schroeder) leads to the development of the broad tapeworm, the growth of which is rapid. In my experiments on human beings the average number of proglottids formed per diem averaged thirty-one to thirty-two for five weeks, with a length of 8 to 9 cm. According to Parona the eggs appear twenty-four days after man has been infected. Zschokke found the average growth in the experimental infection of man between 5·2 and 8·2 cm. per diem, and the person experimented upon by Ijima evacuated a piece of a _Dibothriocephalus latus_, 22·5 cm. in length, only twenty-one days after the infection. [Illustration: FIG. 207.--_Dibothriocephalus latus_: development of egg. 1, segmentation complete; some cells of the blastosphere have migrated through the yolk and have flattened to form _c_, the yolk envelope; others form a layer of flattened cells (_e_) forming the embryophore; the remaining cells (_d_) of the blastosphere form the hexacanth embryo. 2, embryophore (_e_) is becoming thicker. 3, the ciliated embryo has been pressed out of the shell; _s′_, the operculum; _c_, the yolk envelope remaining in the shell (_s_); _y_, the yolk consisting of separate cells. 4, a free-swimming larva much swollen by the water. (After Benham and Schauinsland.)] The “broad tapeworm” is a frequent parasite of man in some districts, but it also occurs in the domestic dog, and on rare occasions is found in the domestic cat (together with _Dibothriocephalus felis_, Crepl.) and fox. French Switzerland and the Baltic Provinces of Russia are the centres of distribution; from the former districts the distribution radiates to France and Italy (Lombardy, Piedmont); from the Baltic Provinces over Ingermanland to Petrograd, over Finland to Sweden (on the shore of the Gulf of Bothnia), in a southerly direction to Poland, and into the Russian Empire and across it to Roumania, and towards the west along the coast of the Baltic Sea to the North Sea, where, however, its frequency considerably diminishes (Holland, Belgium, and the North of France). In Turkestan and Japan the “broad tapeworm” is the most frequent parasite of man; it has been reported in Africa from the vicinity of Lake N’gami as well as from Madagascar; cases, in part at least imported, have also come under observation in North America. [Illustration: FIG. 208.--Plerocercoid of _Dibothricephalus latus_. _A._, with the head evaginated; _B._, with the head invaginated. From the muscle of the pike.] [Illustration: FIG. 209.--A piece of the body wall of the Burbot, _Lota vulgaris_. The tangential section has exposed the muscles of the trunk, with a plerocercoid of _Dibothriocephalus latus_. Natural size.] In Germany _Dibothriocephalus latus_--apart from the fact that it is undoubtedly imported from Switzerland, Russia or Italy--is particularly frequent in East Prussia amongst the inhabitants of the Courland Lagoon district, on the Baltic; it is, moreover, also found in the Province and even in the City of Königsberg. In West Prussia and Pomerania it is very much scarcer. It is also found in Munich and in the vicinity of the Lake of Starnberg (Bollinger). Krabbe found it in 10 per cent. of the sufferers from tapeworms in Denmark; Szydlowski found the ova of this worm in Dorpat in 10 per cent. of the fæces examined; Kruse found the worm in 6 per cent. of _post-mortems_; Kessler, in Petrograd, found the eggs in the fæces in 7·8 per cent.; at _post-mortems_ he found the worms in 1·17 per cent., though Winogradoff only found it in 0·8 per cent. In Moscow, according to Baranovsky, 8·9 per cent. of the fæces examined contained the ova of _Dibothriocephalus_. In the interior and southern provinces of Sweden the worm, according to Lönnberg, is only found sporadically, but, on the other hand, in Angermanland about 10 per cent. of the population is affected; while again in Norbotten the majority of persons are affected, and in Haparanda the entire population (with the exception of infants) harbour this parasite. In Switzerland _D. latus_ is very frequent in close proximity to the lakes of Bieler, Neuchatel, Morat and Geneva (according to Zaeslin 10 to 15 to 20 per cent. of the population are affected); the parasite is less frequent in districts one to four hours removed from these lakes. Of the fish from Swiss lakes examined by Schor those from Lake Geneva were most commonly infected, and especially _Lota_ sp. and _Perea_ sp. The frequency and distribution have, nevertheless, decreased perceptibly in places; at the commencement of the eighteenth century the broad tapeworm was very common in Paris, at the present date it only occurs when imported (Blanchard); in Geneva, also, according to Zschokke, it has become rarer (formerly 10 per cent., now only 1 per cent.). The disturbances produced in man by the presence of broad tapeworms are, as a rule, very trifling; in other cases they produce partly gastric disorders and partly nervous symptoms; in a number of cases, again, they set up severe anæmia, apparently caused by toxins produced by the worms and absorbed by the host. There is no danger of auto-infection, as the larval stage lives only in fishes, not in warm-blooded animals. The case reported by Meschede (ova like those of _Dibothriocephalus latus_ in the brain of a man who had suffered from epilepsy for six years) must be otherwise explained. Human beings, like other hosts, can only acquire the broad tapeworm by ingesting its plerocercoids with the previously mentioned fresh-water fishes; the opportunity for such infection is afforded the more readily by the fact that not only do the lower classes not pay sufficient attention to the cooking of fish, so that all the larvæ that are present may be killed, but also in certain localities the custom exists of eating some parts of these fishes in a raw condition; even the mere handling of the usually severely infected intermediary hosts may occasionally cause infection. The plerocercoids are as well known as, but differ materially in appearance from, the cysticerci (_Cysticercus cellulosæ_) of pig’s flesh. In Germany the occurrence of the plerocercoids of _Dibothriocephalus latus_ has been confirmed in the pike, miller’s thumb and perch of East Prussia, and more particularly in those taken from the Courland Lagoon. The life of _D. latus_ is a very long one (six to fourteen years), as is deduced from persons who have left _D. latus_ regions after they have been infected. According to the experiments of M. Schor, plerocercoids of _D. latus_ placed in slowly warmed water completely lose their movement at 54° to 55° C.; they survive the death of their host for several days; they are killed by low temperatures -3° to +1° C. in two days; strong acids and salt solutions kill them at once, also high temperatures, but all the same at least ten minutes is required in boiling or frying fish in order to kill the plerocercoids with certainty. *Dibothriocephalus cordatus*, R. Lkt., 1863. Syn.: _Bothriocephalus cordatus_, R. Lkt. [Illustration: FIG. 210.--Cephalic end of _Dibothriocephalus cordatus_; on the left viewed sideways, on the right from the dorsal surface, showing a suctorial groove. (After Leuckart.)] Length, 80 to 115 cm.; the head is heart-shaped and measures 2 by 2 mm. The suctorial grooves are on the flat surface; the segments commence close behind the head and increase rapidly in breadth. At only 3 cm. behind the head they are already mature; the greatest breadth attained by them averages 7 to 8 mm., the length 3 to 4 mm.; the number of proglottids averages 600; the most posterior ones are usually square. The uterine rosette is generally formed of six to eight lateral loops. The eggs are operculated and measure 75 µ by 50 µ. _Dibothriocephalus cordatus_ is a common parasite of the seal, the walrus and the dog in Greenland and Iceland, occasionally of man also. No doubt its larva lives in fishes. The statement that _D. cordatus_ also occurs in Dorpat in human beings has been proved erroneous (_Zool. Anzeiger_, 1882, v, p. 46), as also has the report that this worm lives in hares in the neighbourhood of Berlin, whither it was supposed to have been carried by Esquimaux dogs (Rosenkranz in _Deutsch. med. Wochenschr._, 1877, iii, p. 620). The parasite stated by the author to be _D. cordatus_ is _Tænia pectinata_, Goeze, which has been known since 1766. *Dibothriocephalus parvus*, Stephens, 1908. Largest gravid segments 5 by 3 mm. Uterus forms a central rosette with four to five loops on each side of median line. In a proglottid measuring 3·5 by 2·25 mm. the genital atrium is situated 0·4 to 0·5 mm. behind the anterior margin and the uterine opening the same distance behind the genital atrium. Calcareous corpuscles absent in the preserved specimens. Eggs operculated, 59·2 µ by 40·7 µ. Distinguished from _Dibothriocephalus latus_--(1) by the size of gravid segments (the minimum width of gravid segments of _D. latus_ is 10 to 12 mm., so that _D. parvus_ is a much smaller worm); (2) quadrate segments of _D. latus_ measure 6 by 6 mm., those of _D. parvus_ 4 by 4 mm.; (3) by the eggs. From _D. cordatus_ it is distinguished by--(1) _D. cordatus_ has only fifty immature segments, _D. parvus_ has at least 200, possibly more; (2) mature segments of _D. cordatus_ measure 7 to 8 mm., maximum width of _D. parvus_ is 5 mm.; (3) quadrate segments of _D. cordatus_ measure 5 to 6 mm.; (4) _D. cordatus_ has six to eight uterine loops; (5) _D. cordatus_ measures 75 µ to 80 µ by 50 µ. _Habitat._--Intestine of man (Syrian, in Tasmania). Genus. *Diplogonoporus*, Lönnbrg., 1892. Syn.: _Krabbea_, R. Blanch., 1894. The scolex is short and has powerful suctorial grooves; no neck; the proglottids are short and broad; there are two sets of genital organs side by side in each segment, which in all essentials resemble the single one of _Dibothriocephalus_. Parasitic in whales and seals, occasionally in man. *Diplogonoporus grandis*, R. Blanch., 1894. Syn.: _Bothriocephalus_ sp., Ijima et Kurimoto, 1894; _Krabbea grandis_, R. Blanch. Scolex unknown; chain of proglottids over 10 m. in length, 1·5 mm. broad anteriorly, 25 mm. broad posteriorly. The proglottids are very short (0·45 mm.), but 14 to 16 mm. broad. On either side to the right and left of the worm, along the entire ventral surface, there is a longitudinal groove; these grooves are nearer to each other than to the lateral margin; in them lie the genital pores, and they are in the same sequence as in _Dibothriocephalus_; corresponding to the scanty length (0·45 mm.) of the proglottids, the ovary is only developed transversely; the uterus only makes a few loops. Eggs (fig. 195) thick shelled, brown, 63 µ by 48 µ to 50 µ. This parasite has hitherto been observed twice in Japanese. Similar species are known in Cetacea and seals. [Illustration: FIG. 211.--_Diplogonoporus grandis_, Lühe, 1899: ventral view of a portion of the strobila, showing two rows of genital pores and partially extruded cirri. (After Ijima and Kurimoto.)] [Illustration: FIG. 212.--_Diplogonoporus grandis_: ventral view (diagrammatic) of genitalia of left side; _cir_, cirrus; _cir.o_, cirrus opening; _dtg._, vitelline duct; _ov._, ovary; _ovd._, oviduct; _sb._, receptaculum seminis; _ut._, uterus; _ut.o._, uterine pore; _vag._, vagina; _vag.o._, vaginal pore; _vd_, vas deferens. × 150. (After Ijima and Kurimoto.)] *Sparganum*, Diesing, 1854. The term _Sparganum_, invented by Diesing, is used as a group name of larval bothriocephalid Cestodes whose development is not sufficiently advanced to enable them to be assigned to any particular genus. *Sparganum mansoni*, Cobb., 1883. Syn.: _Ligula mansoni_, Cobbold, 1883; _Bothriocephalus linguloides_, R. Lkt., 1886; _Bothriocephalus mansoni_, R. Blanch., 1886. These plerocercoids were discovered in 1882 by P. Manson during the _post-mortem_ on a Chinaman who had died in Amoy, twelve specimens being found beneath the peritoneum and one free in the abdominal cavity. Cobbold described them as _Ligula mansoni_, and Leuckart, who contemporaneously reported a case in Japan, termed them _Bothriocephalus liguloides_. Ijima and Murata reported eight further cases, and Miyake records nine further cases, seven of which are recorded in Japanese literature. [Illustration: FIG. 213.--Cephalic end of _Sparganum mansoni_, Cobb. (After Leuckart.)] [Illustration: FIG. 214.--_Sparganum mansoni_: on the right in transverse section. Natural size. (After Ijima and Murata.)] The plerocercoid, which hitherto alone is known to us, attains a length of 30 cm. and a breadth of 3 to 6 to 12 mm. The ribbon-shaped body is wrinkled, the lateral borders are often somewhat thickened, so that the transverse section has the form of a biscuit; the anterior end is usually wider and has the head provided with two weak suctorial grooves, either retracted or protracted. The parasite makes migrations within the body, and thus may reach the urinary passages; then it is either evacuated with the urine or has to be removed from the urethra; not rarely it causes non-inflammatory tumours on various parts of the skin, which are at times painful and at times vary in size. Nothing is known of its development and origin. *Sparganum proliferum*, Ijima, 1905. Syn.: _Plerocercoides prolifer_, Ijima, 1905; _Sparganum prolifer_, Verdun, Manson, 1907. These plerocercoids produce an acne-like condition of the skin. The condition is really one of capsules in great abundance in the subcutaneous tissue and less so in the corium and in the intermuscular connective tissue. The encapsuled worms in the corium feel like embedded rice grains and raise the epidermis, giving rise to an acne-like condition. Many thousands occur scattered over the body; in Ijima’s Japanese case there were over 10,000 in the left thigh. The worms when they first appear in the skin cause itching. The capsules are ovoid, generally about 1 to 2 mm. in diameter, but they may be smaller and also much larger. The larger ones occur in the subcutaneous tissue. The capsules consist of dense tough connective tissue. Each capsule, as a rule, contains one worm, but as many as seven may occur. The skin of areas that have been long infected is swollen and indurated or adherent, giving a somewhat elephantoid appearance. The subcutaneous tissue is thick and filled with slimy fluid or in other parts sclerosed. [Illustration: FIG. 215.--_Sparganum prolifer_: left with buds, right extended. × 4. (After Ijima.)] [Illustration: FIG. 216.--_Sparganum proliferum._ × 10. (After Stiles.)] _The Worm._--The chief peculiarity is its irregular shape and its reproduction in the larval stage by forming supernumerary heads, which are supposed to wander about the body. The simplest forms are thread-like bodies, flat or round, 3 mm. long and 0·3 mm. in diameter, but they may be 12 mm. long by 2·5 mm. broad. The narrow end is the head, which in life invaginates and evaginates, but there is no indication of any suckers, except an inconstant terminal depression. In addition to these simple forms the most complicated and irregular forms occur, due to the formation of buds (heads) at various parts. The detachment and growth of a head account for the presence of more than one worm in a cyst. The irregularity in form is also increased by the presence in the subcuticular tissue of the worm of _reserve food bodies_. These bodies are supposed to be of this nature and are spherical, 100 µ to 300 µ in diameter, but also much elongated. _Calcareous bodies_ in the Japanese worms were 7·5 µ to 12 µ; in the Florida worms 8·8 µ to 17·6 µ. _Mode of Infection._--Probably from eating uncooked fish. _Distribution._--Japan, Florida. Family. *Dipylidiidæ*, Lühe, 1910. Genus. *Dipylidium*, R. Lkt., 1863. Rostellum retractile, with several rings of alternating hooks; the latter with a disc-like base, having the shape of the thorns of a rose. Genital pores opposite; genitalia double. Testes very numerous in the central field; ovary with two lobes; the vitellaria, which are smaller, behind them; the uterus forms a reticulum, in the network of which the testicular vesicles lie; later on it breaks up into sacs enclosing one or several eggs. The eggs have a double shell. *Dipylidium caninum*, L., 1758. Syn.: _Tænia canina_, L., 1758, p. p.; _Tænia moniliformis_, Pallas, 1781; _Tænia cucumerina_, Bloch, 1782; _Tænia elliptica_, Batsch, 1786; _Dipylidium cucumerinum_, Lkt., 1863. [Illustration: FIG. 217.--_Dipylidium caninum_: on the left, the scolex, neck and the first proglottids; on the right, at the top, a packet of ova; below, hooks of the rostellum, side and front views; below, an ovum. Various magnifications. (After Diamare.)] [Illustration: FIG. 218.--_Dipylidium caninum_; egg showing _a_, egg-shell (vitelline membrane of Moniez); _b_, albuminous coat; _c_, internal shell formed of or secreted by an outer layer of blastomeres (Moniez); _d_, hexacanth embryo. (After Benham and Moniez.)] This worm measures 15 to 35 cm. in length and 1·5 to 3 mm. in breadth. The scolex is small, rhomboidal, and has a club-shaped rostellum on which there are, in three to four rings, forty-eight to sixty hooks resembling rose thorns, the size of those in the foremost being 11 µ to 15 µ and those in the hindmost ring 6 µ. The neck is very short, the most anterior segments broad and short, the middle as long as they are broad; the mature segments are longer than wide (6 to 7 mm. by 2 to 3 mm.), fairly thick, are frequently of a reddish colour, and when cast off resemble cucumber seeds. The genital pores lie symmetrically at the lateral margins; the roundish egg sacs, arising from the uterine reticulum, contain eight to fifteen eggs embedded in a reddish cement substance (in life). The eggs are globular (43 µ to 50 µ,); the embryonal shell (embryophore) is thin, the oncosphere measures 32 µ to 36 µ. Surrounding the embryophore is an albuminous coating, and outside this the thin vitelline envelope (fig. 218). [Illustration: FIG. 219.--_Dipylidium caninum_: central portion of a proglottis. _C.p._, cirrus sac; _V.s._, vitellaria; _Ex.v._, excretory vessels; _T._, testicles lying in the meshes of the uterine reticulum which laterally forms pouches; _O._, ovary; _U._, reticulum of uterus; _V._, vagina and seminal receptacle (below ovary). Magnified. (After Neumann and Railliet.)] [Illustration: FIG. 220.--_Dipylidium caninum_: development of embryo. 1, solid hexacanth embryo; 2, primitive lacuna (_a_) in the embryo; 3, elongation of hinder part, rudiments of sucker and rostellum appearing; 4, “body” and “tail” distinct, (_b_) and (_c_) excretory system; 5, fore-body invaginates into hind-body, excretory bladder has a pore; 6, tail has dropped off; scolex growing up into secondary cavity formed by fore-body; the primitive cavity has been absorbed at stage 4. (After Benham, Grassi and Rovelli.)] _Dipylidium caninum_ is a common intestinal parasite of dogs, in which it grows larger (_Tænia cucumerina_, Bloch) than in cats (_T. elliptica_, Batsch); it has, however, also been found in jackals, as well as in human beings, though in the latter it is of comparatively rare occurrence (twenty-four cases), and almost always affects children, generally of tender age. One-third of all the cases in children were sucklings, about a quarter of all the cases recorded were adults, and these occurred throughout all Europe with the exception of Spain and Italy. [Illustration: FIG. 221.--Larva (cysticercoid) of _Dipylidium caninum_, consisting of body and tail. The latter is solid and bears on it the embryonal spines. The bladder, which was only slightly developed, has disappeared, and the fore-part of the body bearing the rostellum is now seen invaginated into the hind portion. The hooklets are shown in front of the excretory system which has now developed. At a further stage the tail drops off; the head now evaginates, but is still enclosed in a double-walled sac formed by the prolongation upwards on each side of the topmost parts of the body shown in the figure. _Cf._ fig. 220, 6. Enlarged. (After Grassi and Rovelli.)] The proglottids, which leave the intestine spontaneously, are recognizable by the naked eye on account of their form and reddish colour, as well as their two genital pores. As a rule, the presence of this parasite sets up no marked symptom in the patient. The corresponding larval form (cysticercoid) lives in the louse of the dog (_Trichodectes canis_), a fact that was first established by Melnikow and Leuckart; according to Grassi and Rovelli, as well as Sonsino, it also lives in the flea of the dog (_Ctenocephalus canis_) and in the flea of man (_Pulex irritans_), but not in its larva. The adult segments, which also leave the rectum of dogs and cats spontaneously, creep about around the anus and get into the hair, and are thus partly dried and disintegrated. Part of the segments, or the oncospheres released by disintegration, are then taken up by lice and fleas, within which they develop into larvæ (cysticercoids). Dogs and cats are thus infected by their own skin parasites, which they bite and swallow whilst gnawing at their fur. The infection of human beings must occur in an analogous manner, by transmission of the cysticercoids present on the lips or tongue of dogs when the latter lick them, or it may be that the vermin of cats and dogs harbouring cysticercoids are accidentally and directly swallowed by human beings. Family. *Hymenolepididæ*, Railliet and Henry, 1909. Genus. *Hymenolepis*,[282] Weinland, 1858. [282] The genus is by some authors divided into two sub-genera--Hymenolepis, s. str., and Drepanidotænia, Raill. _Drepanidotænia._--Body, broad lanceolate, testes three, female genitalia antiporal beside the testes. Scolex small, with eight hooks. Neck very short, longitudinal muscle bundles very numerous. No accessory sac opening into genital atrium. _Hymenolepis._--Narrow, female genitalia ventral to or between testes. Accessory sac (opening into genital atrium) usually absent. Vas deferens with an external (outside cirrus sac) and an internal (inside cirrus sac) “seminal vesicle.” Three testes in each proglottis. The eggs are round or oval with two to four distinct envelopes. In mammals and birds. *Hymenolepis nana*, v. Sieb., 1852. Syn.: _Tænia nana_, v. Sieb., 1852, _nec_ van Beneden, 1867; _Tænia ægyptiaca_, Bil., 1852; _Diplacanthus-nanus_, Weinld., 1858; _Tænia_ (_Hymenolepis_) _nana_, Lkt., 1863. The worm is 10 to 45 mm. in length and 0·5 to 0·7 mm. in breadth; the head is globular, 0·25 to 0·30 mm. in diameter. The rostellum has a single circlet consisting of twenty-four or twenty-eight to thirty hooks, which are only 14 µ to 18 µ in length. The neck is moderately long; the proglottids are very narrow, up to 200 in number, 0·4 to 0·9 mm. in breadth, and 0·014 to 0·030 mm. in length. The eggs are globular or oval, 30 µ to 37 µ to 48 µ; the oncospheres measure 16 µ to 19 µ in diameter, with two coats, separated by an intervening semi-fluid substance (fig. 224). This species was discovered by Bilharz in Cairo in 1851; it was found by him in great numbers in the intestine of a boy who had died of meningitis. For several years this was the only case, until 1885, since when numerous cases have come to light. Spooner (1873) even reported a case from North America, which may, however, have related to _Hymenolepis diminuta_. In Europe the worm is particularly frequent in Sicily, but it has also been repeatedly observed in North Italy; it has, moreover, been reported from Russia, Servia, England, France, Germany, North and South America, the Philippines, Siam and Japan, in all over 100 cases. Notwithstanding its small size this worm causes considerable disorders in its hosts--mostly children--as it sets up loss of appetite, diarrhœa, various nervous disturbances, and even epilepsy; all these symptoms, however, disappear after the expulsion of the parasites, which are generally present in large numbers. [Illustration: FIG. 222.--_Hymenolepis nana_, v. Sieb. About 12/1. (After Leuckart.)] [Illustration: FIG. 223.--_Hymenolepis nana_: head. Enlarged. (After Mertens.)] [Illustration: FIG. 224.--_Hymenolepis nana_: an egg. Highly magnified. (After Grassi.)] [Illustration: FIG. 225.--Longitudinal section through the intestinal villus of a rat, with the larva (cysticercoid) of _Hymenolepis murina_. Magnified. (After Grassi and Rovelli.)] [Illustration: FIG. 226.--_Hymenolepis nana_ (_murina_): cross section of proglottis from a rat. _c.p_., cirrus sac; _rec. sem._, receptaculum seminis; _s.g._, shell gland; _ov._, ovary; _t._, testis; _cort. par._, cortical parenchyma; _m.l.n._, main lateral nerve; _ex. can._, excretory canal; _y.g._, vitellarium. (After v. Linstow.)] [Illustration: FIG. 227.--_Hymenolepis nana_: longitudinal section of an embryo. _bl.p._, anterior opening of secondary cavity; _caud._, caudal appendage; _pr. cav._, primary cavity; _sec. cav._, secondary cavity. Enlarged. (After Grassi and Rovelli.)] The development as well as the manner of infection is still unknown; Grassi is of opinion that _Hymenolepis nana_ is indeed merely a variety of _Hymenolepis murina_, Duj., which lives in rats. According to Grassi direct development takes place with omission of the intermediate host, but with the retention of the larval stage; that is to say, rats infect themselves directly with _Hymenolepis murina_, by ingesting the mature segments or oncospheres of this species, from which subsequently the small larvæ originate in the intestinal wall (fig. 225); when fully developed they fall into the intestinal lumen and become tapeworms. The identity of the two forms has nevertheless been disputed (Moniez, R. Blanchard, v. Linstow), though their near relationship cannot be denied. Grassi gave mature segments of _Hymenolepis murina_ to six persons, but only one person evacuated a tapeworm. This, however, proves nothing in a district where _Hymenolepis nana_ frequently occurs in man; it was, moreover, not possible to infect rats with segments of _Hymenolepis nana_ (of man). Accordingly this form may represent an independent species, which, however, like _Hymenolepis murina_, also omits an intermediate host. *Hymenolepis diminuta*, Rud., 1819. Syn.: _Tænia diminuta_, Rud., 1819; _Tænia leptocephala_, Crepl., 1825; _Tænia flavopunctata_, Weinld., 1858; _Tænia varesina_, E. Parona, 1884; _Tænia minima_, Grassi, 1886. This species measures 20 to 60 cm. in length, and up to 3·5 mm. in breadth; there are from 600 to 1,000 segments. The head is very small (0·2 to 0·5 mm.), it is club-shaped and has a rudimentary unarmed rostellum; the neck is short; the mature segments are 3·5 mm. in breadth, 0·66 mm. in length; the eggs are round or oval. The outer egg-shell is yellowish and thickened, with indistinct radial stripes; the inner embryonal shell (embryophore) double, thin; the outer layer is somewhat pointed at the poles; oncosphere 28 µ by 36 µ. Between the inner and outer shells is a middle granular layer. [Illustration: FIG. 228.--_Hymenolepis diminuta_: scolex. Magnified. (After Zschokke.)] [Illustration: FIG. 229.--_Hymenolepis diminuta_: two proglottids showing testes (3), ovary and vagina. Slightly enlarged. (After Grassi.)] [Illustration: FIG. 230.--_Hymenolepis diminuta_: egg from man. (After Bizzozero.)] _Hymenolepis diminuta_ lives in the intestine of rats--_Mus decumanus_ (the sewer rat), _Mus rattus_ (the black rat), and _Mus alexandrinus_, rarely in mice; it is occasionally also found in human beings. Weinland described it from specimens collected by Dr. E. Palmer in 1842, in Boston, from a child aged 19 months, as _T. flavopunctata_. A second case relating to a three year old child, from Philadelphia, was only reported in 1889 by Leidy; a third case was simultaneously reported of a two year old girl in Varese (_T. varesina_); and Grassi described another case relating to a twelve year old girl from Catania (Sicily). Sonsino and Previtera reported the same species in Italy, Zschokke in France, Lutz and Magalhães in South America, and Packard in North America: a total of twelve cases, five from America, the rest from Europe (Ransom). According to Grassi and Rovelli the larval stage lives in a small moth (_Asopia farinalis_), as well as in its larva, in an orthopteron (_Anisolabis annulipes_), and in coleoptera (_Acis spinosa_ and _Scaurus striatus_). Experimental infections have been successful on rats as well as on human beings. In America other species of insects may be the intermediary hosts. [Illustration: FIG. 231.--_Hymenolepis diminuta_: cysticercoid from the rat flea (_Ceratophyllus fasciatus_). _a_, remains of primary vesicle; _b_, fibrous layer; _c_, radially striated layer resembling cuticle; _d_, layer of columnar cells; _e_, parenchymatous layer of irregularly disposed cells; _f_, parenchymatous layer. (Stephens, after Nicoll and Minchin.)] Nicoll and Minchin[283] found in the body cavity of 4 per cent. of rat fleas (_Ceratophyllus fasciatus_) the cysticercoid of _Hymenolepis diminuta_. That it belonged to this species was shown by its unarmed rostellum and by feeding; 340 fleas were fed to white rats and fourteen worms obtained, _i.e._, about 4 per cent., thus corresponding to the infection of the fleas. The development in the flea probably begins in the pupal stage, the eggs being ingested by the older flea larvæ. The larva is 0·31 by 0·25 mm.; tail 0·8 mm., scolex 0·075 by 0·09 mm., suckers, 0·055 mm. in diameter. Microscopically it shows--(1) externally a radially striated layer resembling cuticle, (2) a layer of columnar cells, (3) parenchymatous layer continuous with the tail, (4) fibrous layer around the small caudal vesicle, then the parenchymatous scolex at the bottom of the secondary cavity. [283] _Proc. Zool. Soc._, 1911, p. 9. Nicoll and Minchin (_loc. cit._) found a cysticercoid[284] in the rat flea _Ceratophyllus fasciatus_ which was probably that of _Hymenolepis murina_. Body 0·16 mm., tail 0·19 mm., scolex 0·096 mm. in diameter. Rostellum has twenty-three spines in a single row. Length 0·017 mm., handle 0·01 mm., guard 0·007 mm., prong 0·007 mm. Sucker 0·042 mm. Although this cycle, then, for _H. murina_ also exists, it is not probable that rats (or man in the case of _H. nana_ if this be considered distinct) infect themselves in this way, as they hardly ingest all the necessary fleas to account for the massive infection which frequently exists in rats (and man), so that Grassi’s cycle holds good as the predominant method. _Xenopsylla cheopis_ has also been found by Johnston to harbour both cysticercoids in Australia. [284] A third cysticercoid resembling this, but without hooks, has also been found. *Hymenolepis lanceolata*, Bloch, 1782. Syn.: _Tænia lanceolata_, Bloch, 1782; _Drepanidotænia lanceolata_, Railliet, 1892. [Illustration: FIG. 232.--_Hymenolepis lanceolata_. Natural size. (After Goeze.) To the right above, two hooks. 120/1. (After Krabbe.)] [Illustration: FIG. 233.--_Hymenolepis lanceolata_: diagram of female genitalia. _ov._, ovary; _ovd._, oviduct; _rec. sem._, receptaculum seminis; _s.g._, shell gland; _ut._, uterus; _y.g._, vitellarium. (After Wolffhügel.)] The parasite measures 30 to 130 mm. in length and 5 to 18 mm. in breadth; the head is globular and very small; the rostellum is cylindrical, with a circlet composed of eight hooks (31 µ to 35 µ in length). The neck is very short. The short segments increase gradually and equally in breadth, but only a little in length; the female glands lie on the side opposite to that on which the genital pore is situated; the three elliptical testes are on the same side as the pores; the cirrus is armed and slender. The eggs have three envelopes and are oval (50 µ by 35 µ), the external envelope is thin, the middle intermediate layer or envelope is not so marked as in _H. diminuta_, and the internal one is very thin and sometimes has polar papillæ, as in _Hymenolepis diminuta_ and _H. nana_. It inhabits the intestine of the following birds: Domesticated ducks and geese, the Muscovy duck (_Cairina moschata_), white-headed duck (_Erismatura leucocephala_), the pochard (_Nyroca rufina_), and the flamingo (_Phœnicopterus antiquorum_). It has been recorded from Great Britain, France, Denmark, Austria and Germany. Zschokke reports the receipt of two specimens which a twelve year old boy in Breslau evacuated spontaneously at two different times. The corresponding larva, according to Mrázek, lives in fresh water _Cyclops_; according to Dadai it is likewise found in another copepod, _Diaptomus spinosus_, but the hooks of Dadai’s larva differed in size. Family. *Davaineidæ*, Fuhrmann, 1907. Sub-family. *Davaineinæ*, Braun, 1900. Genus. *Davainea*, R. Blanch., 1891. The large scolex is more or less globular, much wider than the rostellum, which is furnished with two rings of very small and numerous hooks. Neck absent, proglottids few, genitalia single. Parasitic chiefly in birds.[285] [285] [The larval stage of the Davaineas occurs in slugs (_Limax_) and snails (_Helix_).--F. V. T.] *Davainea madagascariensis*, Davaine, 1869. Syn.: _Tænia madagascariensis_, Dav.; _Tænia demerariensis_, Daniels, 1895. This worm measures 25 to 30 cm. in length; the head has four large round suckers; the rostellum has ninety hooks (18 µ in length); there are 500 to 700 segments, of which the last 100 are filled with eggs and form half of the entire worm. The segments, when mature, measure 2 mm. in length by 1·4 mm. in breadth; genital pores unilateral; about fifty testes; the uterus consists of a number of loops, which at each side are rolled up into an almost spherical ball; when filled with eggs the convolutions unwind, permeate the segment and then lose their wall; the eggs lying free in the parenchyma become finally surrounded, one, or several together, by proliferating parenchymatous cells; this is how the 300 to 400 egg masses, taking up the entire mature segment, are formed. The globular oncosphere (8 µ) is surrounded by two perfectly transparent shells, the outer of which terminates in two pointed processes. [Illustration: FIG. 234.--Scolex of _Davainea madagascariensis_. The hooks have fallen off. 14/1. (After Blanchard.)] _Davainea madagascariensis_ has hitherto been found in man only (eight times). Davaine described this species from fragments sent to him from Mayotta (Comoro Islands), which were found in two Creole children. Chevreau observed four cases in Port Louis (Mauritius), likewise in children; Leuckart received the first perfect specimen--it was obtained from a three year old boy, the son of a Danish captain, in Bangkok; Daniels, at the _post-mortem_ of an adult native of George Town, Guiana, found two specimens (_Tænia demerariensis_); and finally Blanchard describes another perfect specimen which was in Davaine’s collection of helminthes in Paris, and which was obtained from a little girl 3 years old, of Nossi-Bé (Madagascar). The intermediate host is unknown. *Davainea (?) asiatica*, v. Linst., 1901. Syn.: _Tænia asiatica_, v. Linstow. There exists only one headless specimen of this species, which is not quite adult, and which is preserved in the Zoological Museum of the Imperial Academy of Science in Petrograd. It came from a human being and was found by Anger in Aschabad (Asiatic Russia, near the northern frontier of Persia). The specimen measures 298 mm. in length. The breadth anteriorly is only 0·16 mm., the posterior part measures 1·78 mm. across. The number of segments is about 750. The genital pores are unilateral; the testes are globular and lie in a dorsal and ventral layer in the medullary layer; the cirrus pouch is pyriform, 0·079 mm. in length and 0·049 mm. in breadth; the female glands lie in the fore-part of the segments, the ovary reaching to the excretory vessels; the vitellarium is small and round. The vagina has a large fusiform receptaculum seminis; the uterus breaks up into sixty to seventy large, irregularly polyhedric eggsacs. Family. *Tæniidæ*, Ludwig, 1886. Genus. *Tænia*, L., 1758.[286] With the characters of the family. In the genus Cladotænia recognized by some authors, the testes encroach on the mid field and the uterine stem reaches the anterior end of the segment. [286] The Greeks termed the tapeworms ἕλμινθες πλατεῖαι, more rarely χηρία (= fascia); the Romans called them _tænia_, _tinea_, _tæniola_, later _lumbrici_, usually with the addition _lati_, to distinguish them from the _Lumbrici teretes_ (_Ascaridæ_). The proglottids were called _Vermes cucurbitini_; the cysticerci χάλαζαι (hailstones), later hydatids. Plater (1602) was the first to differentiate _Tænia intestinorum_ (= _Bothriocephalus latus_) amongst the _Lumbrici lati_ of man from _Tænia longissima_ (= _Tænia solium_). The term _solium_ was already used by Arnoldus Villanovanus, who lived about 1300; and, according to him, it signifies “cingulum” (belt, chain), while N. Andry, in 1700, traces this word from “solus,” because the worm occurs always singly in man. Leuckart and Krehl derive the word “solium” from the Syrian “schuschl” (the chain), which in Arabian has become “susl” or “sosl,” and in Latin has become “sol-ium.” What Linnæus described under the term _Tænia solium_ was really _Tænia saginata_; the latter was first distinguished by Goeze, but was forgotten until Küchenmeister, in 1852, again called attention to the differences. *Tænia solium*, L., _p. p._, 1767. Syn.: _Tænia cucurbitina_, Pall., 1781; _Tænia pellucida_, Goeze, 1782; _Tænia vulgaris_, Werner, 1782; _Tænia dentata_, Gmel., 1790; _Halysis solium_, Zeder, 1800; _Tænia humana armata_, Brera, 1802; _Tænia_ (_Cystotænia_) _solium_, Lkt., 1862. The average length of the entire tapeworm is about 2 to 3 m., but may be even more; the head is globular, 0·6 to 0·8 to 1·0 mm. in diameter. The rostellum is short with a double circlet of hooks, twenty-two to thirty-two in number, usually twenty-six to twenty-eight; large and small hooks alternate regularly; the length of the large hooks is 0·16 to 0·18 mm., of the small ones 0·11 to 0·14 mm. The rostellum is sometimes pigmented. The suckers are hemispherical, 0·4 to 0·5 mm. in diameter. The neck is fairly thin and long (5 to 10 mm.). The proglottids, the number of which averages from 800 to 900, increase in size very gradually; at about 1 m. behind the head they are square and have the genitalia fully developed. Segments sufficiently mature for detachment measure 10 to 12 mm. in length by 5 to 6 mm. in breadth. The genital pores alternate fairly evenly at the lateral margin a little behind the middle of each segment. The fully developed uterus consists of a median trunk, with seven to ten lateral branches at either side, some of which are again ramified. The eggs are oval, the egg-shell very thin and delicate; the embryonal shell (embryophore) is thick, with radial stripes; it is of a pale yellowish colour, globular, and measures 31 µ to 36 µ in diameter; the oncospheres, with six hooks, are likewise globular, and measure 20 µ in diameter (fig. 238). Malformations are not so common as in _T. saginata_; they consist in two or several proglottids being partly or entirely fused, formation of single club-shaped segments, fenestration of long or short series of segments and so-called double formation, in which the head has six suckers and the segments exhibit a *Y*-shaped transverse section. The oncospheres occasionally also possess more than six hooklets. Very slender specimens have led to the description of a particular species or variety (_T. tenella_). In its fully developed condition _T. solium_ is found exclusively in man; the head is usually attached in the anterior third of the small intestine and the chain, in numerous convolutions, extends backwards; a few mature detached proglottids usually lie at the most posterior part, and these are usually evacuated during defæcation. In exceptional cases single proglottids or whole worms may reach contiguous organs if abnormal communications with them exist; thus they may reach the abdominal cavity and the urinary bladder, or they may be found in a so-called worm abscess of the peritoneum; occasionally, in vomiting, single segments or several together may be brought up. Exceptionally it induces severe anæmia. [Illustration: FIG. 235.--Two fairly mature proglottids of _Tænia solium_, showing ovaries (one bi-lobed), vitellaria, central uterine stem, cirrus and vas deferens (above), vagina (below), testes (scattered), longitudinal and transverse excretory vessels.] [Illustration: FIG. 236.--Head of _Tænia solium_. 45/1.] The _larval stage_ (_Cysticercus cellulosæ_) that gives rise to _Tænia solium_ lives normally in the intramuscular connective tissue and other organs of the domestic pig, but it is known to exist also in a few other mammals, such as the wild boar, the sheep,[287] the stag, dog, cat, brown bear and monkey, as well as in man. The cysticercus of the pig is an elliptical vesicle with a longitudinal diameter of 6 to 20 mm., and a transverse diameter of 5 to 10 mm. [287] The larvæ which on rare occasions are found in the muscular system of sheep are either strayed specimens of _Cysticercus tenuicollis_, which normally develop in organs of the abdominal cavity, and appertain to _Tænia marginata_ of the dog, or actually _Cysticercus cellulosæ_. (_Cf._ Bongert, in _Zeitschr. f. Fleisch- u. Milchhyg._, 1899, ix, p. 86.) Even with the naked eye a white spot may be observed in the centre of the long equator, this being the invaginated head; it is easy to make it project by pressing on the vesicle (after tearing off with the finger-nail the investing connective tissue), and on examining it under the microscope one can convince oneself that it corresponds with the head of _Tænia solium_. [Illustration: FIG. 237.--Large and small hooks of _Tænia solium_. 280/1. (After Leuckart.)] [Illustration: FIG. 238.--_Tænia solium._ 21, Egg with external membrane; 22, without (embryophore). (After Leuckart.)] [Illustration: FIG. 239.--Two mature proglottids of _Tænia solium_ with fully developed uterus. 2/1.] Numerous experiments have proved that the _Cysticercus cellulosæ_ of the pig, if introduced into the intestine of man, grows to a _Tænia solium_ (Küchenmeister, 1855; Humbert, 1856; Leuckart, 1856; Hollenbach, 1859; Heller, 1876); the cysticercus has frequently also been cultivated purposely by feeding pigs with mature proglottids of _T. solium_ (P. J. van Beneden, 1853; Haubner and Küchenmeister, 1855; Leuckart, 1856; Mosler, 1865; Gerlach, 1870; etc.), but success did not attend the efforts to make _Cysticercus cellulosæ_ establish themselves in the intestines of pigs, dogs, guinea-pigs, rabbits and monkeys (_Macacus cynomolgus_), and so become adult Tæniæ; the attempts, also, to infect dogs with cysticerci by means of ova were likewise, as a rule, abortive.[288] [288] According to Gerlach only young pigs (up to 6 months old) are capable of infection, and perhaps the failure may have been due to the animals chosen for experiment being of the wrong age. The development of _Cysticercus cellulosæ_ takes two and a half to three or four months; it is not known how long the cysticerci remain alive in animals; not uncommonly they perish at earlier or later stages, and become calcified or caseated. Extracted cysticerci die in water at a temperature of 47° to 48° C., in flesh at normal temperature they remain alive for twenty-nine days or more. On account of the present rapid means of pickling and smoking meat, the cysticerci as a rule are not killed, also the effect of cold on them for some time in cold chambers of slaughterhouses is not lethal, but freezing is fatal (Ostertag). There is not the least doubt that human beings are almost exclusively infected with _Tænia solium_ by eating pork containing cysticerci in a condition that does not endanger the life of the cysticerci. The infection may likewise be caused in man by eating the infected meat of other animals subject to this species of bladder worm, mainly, as a matter of fact, deer and wild boar. The frequency of cysticerci in pigs’ flesh has considerably decreased since the introduction of meat inspection; in the Kingdom of Prussia there was on an average 1 infected pig to every 305 slaughtered between 1876 to 1882; from 1886 to 1889, there was 1 to 551; from 1890 to 1892, there was 1 to 817; in 1896, 1 to 1,470; and in 1899, 1 to 2,102; in the Kingdom of Saxony in 1894 there was 1 infected pig to every 636; in 1895 there was 1 to every 2,049, and in 1896 only 1 infected pig was found of 5,886 slaughtered. In South Germany pigs with cysticerci are very rare, but are more frequent in the eastern provinces of Prussia; in 1892 the number of infected pigs compared with the total slaughtered was as follows:-- In the district of Marienwerder 1 : 28 " " Oppeln 1 : 80 " " Königsberg 1 : 108 " " Stralsund and Posen 1 : 187 " " Danzig, Frankfort a. O. and Bromberg 1 : 250 As compared with the district of Arnsberg 1 : 865 " " " Coblenz 1 : 975 " " " Düsseldorf 1 : 1,070 " " " Münster and Wiesbaden 1 : 1,900 The average for the whole of Prussia in the same year was 1 : 1,290; for the eastern provinces, on the other hand, 1 : 604. Even more unfavourable are the proportions in Russian Poland (over 1 per cent. of pigs measly), in Prague (over 3 per cent.), in Bosnia and Herzegovina (6 to 7 per cent.). The cause for this is most likely attributable to the manner in which the pigs are kept. When allowed to be in the farmyards of the small farmers for the whole day, or allowed to wander in the village streets and pasture lands, they are more liable to take up the oncospheres of the _T. solium_ than when shut up in good pig-styes. The geographical distribution of _T. solium_ generally corresponds with that of the domestic pig and the custom of eating pork in any form insufficiently cooked or raw. There are, or were, some isolated districts in Germany, France, Italy and England where the “armed tapeworm” was frequent (for instance, Thuringia, Brunswick, Saxony, Hesse, Westphalia, whereas it is and was very scarce in South Germany); it is thus easily understood why it occurs very rarely in the East, in Asia and in Africa, in consequence of the Mahommedans, Jews, etc., not eating pork. In North America, also, _T. solium_ is very rare; the tapeworm which is known there by this name is generally _T. saginata_, Stiles. During the last decade _T. solium_ infection has, however, very markedly decreased in North and East Germany in consequence of the precautions exercised by the public in the choice of pork to avoid trichinosis, especially, however, because measly meat must be sold as such and must be thoroughly cooked before being placed on the market; indeed, if badly infected it may not be sold for food, but can be turned to account for industrial purposes. The occurrence of _Cysticercus cellulosæ_ in man has been known since 1558 (Rumler, _Obs. med._, liii, p. 32); there is hardly an organ in man in which cysticerci have not been observed at some time; they are most frequently found in the brain,[289] where they grow to a variety known as _Cysticercus racemosus_; next in frequency they are found in the eye, in the muscular system, in the heart, in the subcutaneous connective tissue, the liver, lungs, abdominal cavity, etc. The number of cysticerci observed in one man varies between a few and several thousands. Of the sexes, men are most subject (60 to 66 per cent. of the number attacked). The disturbances caused in man by cysticerci vary according to the nature or position of the organs attacked; when situated in the cerebral meninges they have the same effect as tumours. [289] Dressel, for instance, examined eighty-seven persons suffering from cysticercus, and found it seventy-two times in the brain, thirteen times in the muscles; K. Müller, in thirty-six cases, found it twenty-one times in the brain, twelve times in the muscles, three times in the heart; Haugg, in twenty-five cases, found it thirteen times in the brain, six times in the muscles, twice in the skin, etc. According to Graefe, amongst 1,000 ophthalmic cases in Halle and Berlin, there was one with cysticercus in the eye; in Stuttgart there was only one in 4,000, in Paris one in 6,000, and in Copenhagen one in 8,000. During the last decades, however, these cases have also become less common. In Rudolphi’s time 2 per cent. of _post-mortems_ in Berlin showed cysticerci; in the ’sixties, according to Virchow, about the same; in 1875 the number fell to 1·6 per cent.; in 1881 to 0·5 per cent.; in 1882 to 0·2 per cent.; in 1900 to 0·15 per cent., and in 1903 to 0·16 per cent. Hirschberg between 1869 and 1885 discovered cysticerci in the eye seventy times in 60,000 ophthalmic cases, but during the following six years the parasite was only present twice amongst a total of 46,000 cases of ophthalmic diseases, and since 1895 no ophthalmic case has been met with. The infection of human beings with the cysticerci can only take place by the introduction of the oncospheres of _Tænia solium_ into the stomach with vegetable foods, salads that have been washed in impure water containing oncospheres, also by drinking contaminated water; the carriers of _T. solium_, moreover, infect themselves still more frequently through uncleanliness in defæcation, the privies in public localities and many private houses affording striking testimony of this. The minute oncospheres can thus easily reach the fingers and thence the mouth (as in twirling the moustache, biting the nail). More rarely a third manner of transmission or internal auto-infection may possibly take place, as when, in the act of vomiting, mature proglottids near the stomach are drawn into it; the oncospheres or segments there retained are then in the same position as if they had been introduced through the mouth. On account of these dangers of internal or external auto-infection, it is therefore the duty of the medical attendant, after recognizing the presence of tapeworms, to expel them,[290] and in doing so to employ every possible means to prevent vomiting setting in; it is, however, equally important to take the necessary steps to destroy the parasites evacuated. It may be incidentally mentioned that in using certain remedies the scolex not rarely remains in the intestine; the cure in such cases has not been accomplished, as the scolex again produces new proglottids, and after about eleven weeks the first formed ones are again mature and appear in the fæces. [290] The diagnosis as a rule is not difficult; the patients themselves frequently observe the pumpkin seed-like segments in the fæces. But in such cases the diagnosis must still be confirmed. In other cases the discovery of the oncospheres in their embryonal shells (embryophores), which cannot be confounded with the other constituents of the fæces, gives complete certainty, although the differential diagnosis between _T. solium_ and _T. saginata_ is hardly possible from the embryophores; but, if evacuated segments are placed between two slides and lightly pressed, the species is easily recognizable by the shape of the uterus (_cf._ figs. 239 and 241). Amongst the cysticerci also many malformations appear; thus absence of the rostellum and the hooks, or double formation with six suckers, or abnormalities of growth on account of the surroundings, which have had a special name given to them, _viz._, _Cysticercus racemosus_, Zenk. (= _C. botryoides_, Hell.; _C. multilocularis_, Kchnmstr.); these forms are more especially found at the base of the brain, are irregularly ramified and often without the head. A certain interest is attached to those forms that have led to the establishment of a distinct species:-- *Cysticercus acanthotrias*, Weinld., 1858. In making the autopsy of a white Virginian woman who had died of phthisis, a cysticercus was found in the dura mater, and eleven or twelve specimens in the muscles and subcutaneous tissue. Weinland and Leuckart, who examined the specimens, found that they resembled _Cysticercus cellulosæ_ in form and size, but that they carried on the rostellum a triple crown, each consisting of fourteen to sixteen hooks, which differed from the hooks of _C. cellulosæ_ or of _Tænia solium_ by the greater length of the posterior root process and the more slender form of the hooks; the large hooks measured 0·153 to 0·196 mm., the medium-sized hooks, 0·114 to 0·14 mm., and the small ones 0·063 to 0·07 mm. On account of these differences a distinct species of cysticercus was established, and this naturally presupposed a corresponding species of Tænia (_T. acanthotrias_, Lkt.); this could be done with justice so long as the case remained isolated, _i.e._, in America, as there was the possibility of the corresponding Tænia being found. In this respect, however, the position has changed; Delore first described a cysticercus the size of a nut from the biceps muscle of the arm of a silk-worker in Lyons; according to Bertolis this specimen possessed hooks of three different sizes, the dimensions of which corresponded with the figures given by Weinland and Leuckart; the correctness of the diagnosis could hardly be doubted, as Bertolis was known to be a very exact observer. A second case has become known through Cobbold, who regards a specimen of a cysticercus in Dallinger’s collection as likewise belonging to _Cysticercus acanthotrias_; this specimen also came from a man’s brain; finally a third case, also from France, has been published by Redon. This author, amongst numerous _C. cellulosæ_ of a man, found one that had forty-one hooks in three rows, and he was the first to express the opinion that _C. acanthotrias_ does not represent a distinct species, but is only an abnormality of _C. cellulosæ_. This view was also taken by Blanchard and Railliet, and is probably correct, as the discovery of the large corresponding Tænia furnished with three rows of hooks is not to be expected in European beasts of prey, and in Redon’s case _C. acanthotrias_ as well as _C. cellulosæ_ occurred simultaneously. The duration of life of _C. cellulosæ_ in man is very long; cysticerci of the eye have been known to persist for twenty years, and in cysticercus of the brain ten to nineteen years may elapse from the first appearance of cerebral symptoms until death. Dead cysticerci may shrivel up or become calcified, perhaps also undergo fatty degeneration and then absorption. Finally, it may be mentioned that if particular proof is required that _C. cellulosæ_ of man belongs to the cycle of development of the _Tænia solium_, such proof has been furnished by Redon. NOTE.--_Tænia tenella_, mentioned on p. 332, was ascribed by Cobbold to cysticerci of the muscular system of sheep. It has, however, been demonstrated that these cysticerci belong to the cycle of development of _Tænia marginata_ (dog) (_Cysticercus tenuicollis_, from the omentum of sheep); but as already stated _C. cellulosæ_ also occurs in sheep. Chatin himself swallowed the cysticercus, which Cobbold termed _C. ovis_, without causing a Tænia to develop in his intestine. Müller also vainly sought to induce infection with _C. tenuicollis_ in his own person. On the other hand, the feeding of a dog with _Cysticercus ovis_ resulted in the production of _Tænia marginata_. *Tænia bremneri*, Stephens, 1908. Characterized by the large size of the gravid segments. The largest was 32 by 9 mm. Smallest 21 by 6 mm. Average 28·6 by 8·5 mm. Mode 21 by 6 mm. Uterine branches twenty-two to twenty-four in number. Calcareous bodies numerous, 15·2 µ in diameter. Eggs maximum 45·6 µ by 41·8 µ. Smallest 34·2 µ by 30·4 µ. Mode 38 µ by 30·4 µ. *Tænia marginata*, Batsch, 1786. Syn.: T. e. _Cysticerco tenuicolli_, Küchenmeister, 1853. This species, which in structure resembles _Tænia solium_, lives in the intestine of the dog and the wolf. It attains 1·5 to 4 m. in length, possesses a double crown of thirty to forty hooks, on an average thirty-six to thirty-eight hooks, and in its larval stage (_Cysticercus tenuicollis_) lives in the peritoneal cavity of ruminants and the pig, occasionally in the monkey and squirrel. [Illustration: FIG. 240.--Large and small hooklets of _Tænia marginata_. 280/1. (After Leuckart.)] It is included in this work because, according to one statement, _C. tenuicollis_ is supposed to have been observed in man in North America; but the case is not quite certain, as the number of hooks was less than in _C. tenuicollis_ and coincided with _C. cellulosæ_, although the size of the cysticercus appeared to point to _C. tenuicollis_. A yet earlier statement of Eschricht, that _Cysticercus tenuicollis_ had been observed in Iceland in the liver of a man, is undoubtedly due to an error. *Tænia serrata*, Goeze, 1782. This parasite attains a length of from 0·5 to 2 m., possesses a double crown of thirty-four to forty-eight (mostly forty) hooks. It lives exclusively in the intestine of the dog, the corresponding cysticercus (_Cysticercus pisiformis_) living in the mesentery of the hare and rabbit. We mention this species with all reserve amongst the parasites of man, because Vital states that he has observed it twice in Constantine (Algeria) in human beings. The data, however, are not sufficient to characterize the species. It is highly probable that they relate to _Tænia solium_. Galli-Valerio even swallowed five specimens of _Cysticercus pisiformis_, but without result. *Tænia crassicollis*, Rud., 1810. I only mention this species from the intestine of the domestic cat because Krabbe regards its occurrence in man as possible. It attains a length of 60 cm. and is armed; its cysticercus (_Cysticercus fasciolaris_) lives in the liver of mice and rats. In Jutland, according to Krabbe, chopped-up mice (spread on bread) are eaten raw, being a national remedy for retention of urine, and this custom affords the possibility of the introduction of _C. fasciolaris_ into the intestine of man (_Nord. med. Arkiv_, 1880, xii). *Tænia saginata*, Goeze, 1782. Syn.: _Tænia solium_, L., 1767 (_pro parte_); _Tænia cucurbitina_, Pallas, 1781 (p.p.); _Tænia inermis_, Brera, 1802. Moquin-Tandon, 1860; _Tænia dentata_, Nicolai, 1830; _Tænia lata_, Pruner, 1847; _Bothriocephalis tropicus_, Schmidtmuller, 1847; _Tænia mediocanellata_, Küchenmeister, 1855; _Tænia zittavensis_, Küchenmeister, 1855; _Tænia tropica_, Moquin-Tandon, 1860; _Tænia_ (_Cystotænia_) _mediocanellata_, Leuckart, 1863. The length of the entire tapeworm averages 4 to 8 to 10 m. and more, even up to 36 m. According to Bérenger-Feraud it attains a length of 74 m. (?) The head is cubical in shape, 1·5 to 2 mm. in diameter; the suckers are hemispherical (0·8 mm.) and are frequently pigmented; there is a sucker-like organ in place of the rostellum, and this also is frequently pigmented. The neck is moderately long and about half the breadth of the head; the proglottids, the number of which averages more than 1,000, gradually increase in size; the mature detached segments are shaped exactly like pumpkin-seeds, and are about 16 to 20 mm. in length and 4 to 7 mm. in breadth. The genital pores alternate irregularly and are situated somewhat behind the middle of the lateral margin. There are twenty to thirty-five lateral branches at each side of the median trunk of the uterus, and these again ramify. The eggs are more or less globular, the egg-shell frequently remains intact and carries one or two filaments; the embryonal shell (embryophore) is thick, radially striated, is transparent and oval; it is 30 µ to 40 µ in length, and 20 µ to 30 µ in breadth. Several segments simultaneously are usually passed spontaneously with defæcation. [Illustration: FIG. 241.--Mature segment of _Tænia saginata_, G., with distended uterus. 2/1.] [Illustration: FIG. 242.--Cephalic end of _Tænia saginata_ in the contracted condition. 8/1.] [Illustration: FIG. 243.--_Tænia saginata._ 19, egg with external shell. 20, without (embryophore). (After Leuckart.)] Malformations are not uncommon, and resemble those of _Tænia solium_; a triangular form has been termed _T. capensis_ by Küchenmeister, and _T. lophosoma_ by Cobbold, names that naturally possess as little value as does the term _T. fenestrata_ for fenestrated specimens. Moreover, _T. solium_, var. _abietina_, Weinld., 1858, which was evacuated by an Indian, was probably a _T. saginata_ with somewhat close uterine branches. It is regarded by Stiles and Goldberger as a doubtful subspecies. _T. saginata_ in its adult condition lives exclusively in the intestinal canal of man.[291] The corresponding cysticercus is _Cysticercus bovis_, and is found almost exclusively in the ox; it is small, 7·5 to 9 mm. in length and 5·5 mm. in breadth, may easily escape notice, and requires from three to six months for its development. Numerous experiments have confirmed the connection of _Cysticercus bovis_ with _Tænia saginata_; indeed, the cysticercus was only discovered by feeding experiments after attention had been called to the ox as the probable intermediary host of this Tænia. [291] Abnormal migrations of this species have also been known. Compare, amongst others, Stieda, A., “Durchbohr. d. Duod. u. d. Pancreas durch eine Tænia,” _Centralbl. f. Bakt., Path. und Infektionsk._, 1900, xxviii (1), p. 430. Medical men observed that weakly children who were ordered to eat raw scraped beef to strengthen them contracted _T. saginata_. It was found, moreover, that Jews, who are prohibited from eating pork from religious motives, suffered especially from _T. saginata_; when _T. solium_ was found to occur in a Jew he often confessed to having eaten pork; and finally it was found that certain nations--for instance, the Abyssinians--frequently harbour _T. saginata_, and only eat beef--raw by preference. These observations led Leuckart, in 1861, to feed young calves with the proglottids of _T. saginata_ in order to discover the corresponding cysticercus, which was then not known. This experiment was successful. Similar experiments, with similar results, were then conducted by Mosler (1863), Cobbold and Simonds (1864 and 1872), Röll (1865), Gerlach (1870), Zürn (1872), Saint Cyr, Jolicœur (1873), Masse and Pourquier (1876), and Perroncito, in 1876. The attempts to infect goats, sheep, dogs, pigs, rabbits and monkeys were unsuccessful. Only Zenker and Heller were able to infect kids, and Heller infected one sheep, but these are exceptions. [Illustration: FIG. 244.--A piece of the muscle of the ox, with three specimens of _Cysticercus bovis_. Natural size. (After Ostertag.)] Artificial infections of human beings with _Cysticercus bovis_ to obtain the tapeworm were less numerous, and indeed quite superfluous, yet this was also done by Oliver (1869) in India, and Perroncito (1877) in Italy. The experiments of the latter prove that the extracted cysticerci of the ox certainly perish in water at 47° to 48° C. It is a remarkable circumstance that, at least as regards Central Europe, _C. bovis_ in the ox, after natural infection, was so seldom found that almost every case was published as a rarity; whereas the Tænia is very frequent in man. The reason for this is that in Germany cattle are not severely infected, and that the small, easily dried-up cysticerci easily escape notice in the large body of the host. Hertwig, the late director of the town cattle market in Berlin, in 1888, pointed out that the cysticercus of the ox is found chiefly in the musculi pterygoide externi and interni, and since that time a far greater number of infected oxen have been found in Berlin. ---------+----------------+----------+------------ Year | Number of oxen | Infected | Proportion | slaughtered | | ---------+----------------+----------+------------ 1888–89 | 141,814 | 113 | 1 : 1,255 1889–90 | 154,218 | 390 | 1 : 395 1890–91 | 124,593 | 263 | 1 : 474 1891–92 | 136,368 | 252 | 1 : 541 1892–93 | 142,874 | 214 | 1 : 672 ---------+----------------+----------+------------ Since 1892 an increase has taken place in the number of oxen infected with cysticercus, but this is probably attributable to the more general and searching examinations. In the slaughter-houses of Prussia the number of infected beasts was as follows:-- 1892 567 1893 686 1894 748 1895 1,143 1896 1,981 1897 2,629 The condition was most frequent in Neisse (3·2 to 4 per cent.), Eisenach (1·91 per cent.), Ohlau (1·57 per cent.), Oels i. Schles. (1 per cent.), Marienwerder (0·34 to 1·2 per cent.). The flesh of oxen only slightly infected (containing not more than ten living cysticerci) is sold in pieces of not more than 5 lb. to consumers after having been rendered innocuous by cooking, or by pickling for twenty-one days in 25 per cent. salt brine, or hanging for twenty-one days in suitable refrigerators; oxen in which only one cysticercus is found are allowed free commerce, and those strongly infected (_i.e._, containing more than ten living cysticerci) may only be used for industrial purposes. It is a striking fact that more bulls than cows are infected (according to Reissmann, in Berlin, from 1895 to 1902, 0·446 per cent. bulls, 0·439 per cent. oxen, and 0·262 per cent. cows), the explanation of which, according to Ostertag, is that most oxen are killed when young, when also infection most readily takes place, and, further, that the larva later on in life can be completely atrophied. The cysticercus of the ox has hitherto been found in man on very rare occasions. Arndt (_Zeitschr. f. Psychiat._, xxiv) mentions a case in the brain, Heller in the eye, and Nabiers and Dubreith also in the brain (_Journ. méd. Bordeaux_, 1889–1890, p. 209); but the diagnoses are not quite certain, as absence of hooks occasionally occurs in _Cysticercus cellulosæ_. _Tænia saginata_ is the most frequent tapeworm of man (with the exception of _Dibothriocephalus latus_ in a few districts), and the parasite is widely distributed over the surface of the globe; it has been known in the East for ages, so far as data are available; it is frequent in Africa, America, and Europe. Its frequency has perceptibly increased during the last few years, but a decrease should soon take place in consequence of the extent and improvement of the official inspection of meat. The following table shows the relative frequency of the Cestodes of man:-- ----------------+---------+----------+----------+-------+------+-------+-------- | |Number of | _T. | _T. |_Dibr.|_Dipyl.|Undeter- Author | Year | cases |saginata_ |solium_|latus_|canin._| mined ----------------+---------+----------+----------+-------+------+-------+-------- Parona (Milan) | 1899 | 150 | 121 | 11 | 4 | -- | 14 Parona (Italy) | 1868–99 | 513 | 397 | 71 | 26 | -- | 19 Krabbe (Denmark)| 1869 | 100 | 37 | 53 | 9 | 1 | -- " " | 1869–86 | 200 | 153 | 24 | 16 | 8 | -- " " | 1887–95 | 100 | 89 | -- | 5 | 6 | -- " " |1896–1904| 50 | 41 | 1 | 5 | 3 | -- Blanchard | 1895 | ? | 1,000 | 21 | -- | -- | -- (Paris) | | | | | | | Stiles | 1895 |{more than|more than}| -- | 3 | -- | -- (United States)| |{ 300 | 300 }| | | | Schoch | 1869 | 19 | 16 | 1 | 2 | -- | -- (Switzerland) | | | | | | | Zaeslein | 1881 | ? | 180 | 19 | ? | | (Switzerland) | | | | | | -- | -- Kessler | 1888 | ? | 22 | 16 | 47 | -- | -- (Petrograd) | | | | | | | Mosler | 1894 | 181 | 112 | 64 | 5 | -- | -- (Greifswald) | | | | | | | Bollinger | 1885 | 25 | 16 | 1 | 8 | -- | -- (Munich) | | | | | | | Vierordt | 1885 | 121 | 113 | 8 | -- | -- | -- (Tübingen) | | | | | | | Mangold | 1885–94 | 128 | 120 | 6 | 8 | -- | -- (Tübingen) | | | | | | | ----------------+---------+----------+----------+-------+------+-------+-------- *Tænia africana*, v. Linst., 1900. [Illustration: FIG. 245.--Mature segment of _Tænia africana_. The ovary is in the middle, and behind it are the shell gland and vitellarium; at the sides are the testicles, and externally the excretory canals; the cirrus pouch, the vas deferens and the vagina are on the left. Magnified. (After v. Linstow.)] This worm measures over 1·3 m. in length. The segments are all broader than they are long. The scolex is unarmed and is provided with an apical sucker (0·16 mm.). The parasite measures 1·38 mm. in breadth, 1·03 mm. in width; the suckers measure 0·63 mm. in diameter. The neck is very short and somewhat broader than the scolex; number of segments about 600; the hindmost segments measure 7 mm. in length and 12 to 15 mm. in breadth. The genital pores alternate irregularly in the middle of the lateral margin; the testes are very numerous and occupy the entire medullary layer; the vas deferens is much convoluted; the cirrus pouch is pyriform and thick walled; the cirrus and vagina are beset with bristles directed outwards; the receptaculum seminis is fusiform; the ovary is large and double, and consists of radially placed club-shaped tubes that do not anastomose and do not branch; the vitellarium is at the posterior border of the proglottids, the round shell gland in front of it; the uterus consists of a median trunk and fifteen to twenty-four non-ramified lateral branches on each side; the embryonal shell is thick and has radial stripes--it may be round (31·2 µ to 33·8 µ) or oval (39 µ, by 33·8 µ); the spines of the oncospheres measure 7 µ to 8 µ in length (fig. 197). [Illustration: FIG. 246.--Proglottis of _Tænia africana_, with uterus. Magnified. (After v. Linstow.)] [Illustration: FIG. 247.--Head of _Tænia africana_; apical surface. Magnified. (After v. Linstow.)] At present only two specimens are known; they came from a black soldier from the vicinity of Lake Nyasa. The cysticercus is unknown; perhaps it lives in the zebu, the flesh of which the Askaris are in the habit of devouring uncooked. *Tænia confusa*, Ward, 1896. Length 8·5 m., breadth about 5 mm. The scolex is unknown; there is no neck; number of proglottids 700 to 800, always longer than they are broad; the hindmost measure 35 mm. in length, 4 to 5 mm. in breadth; the genital pores alternate irregularly behind the middle of the lateral margin; testicles numerous; vas deferens not much coiled; the cirrus pouch thick walled, elongated and club-shaped, with globular vesicula seminalis; the cirrus is beset with little hairs; the receptaculum seminis is globular; ovary small, double; each half is bean-shaped; vitellarium narrow, triangular; shell gland globular; uterus with median trunk and fourteen to eighteen short ramified lateral branches on either side. The embryophores are oval (39 µ by 30 µ), thick and radially striated. [Illustration: FIG. 248.--_Tænia confusa_: mature segment showing central uterine stem, bilobed ovary, globular shell gland, triangular vitellarium, scattered testes, cirrus, vas deferens, and vagina. 15/1. (After Guyer.)] [Illustration: FIG. 249.--_Tænia confusa_: gravid segment. 25/1. (After Ward.)] Of this species only two specimens have been recorded; they occurred in human beings and were sent at different times to the first describer of them by a doctor in Lincoln (Nebr.). Perhaps _Tænia solium_, var. _abietina_, Weinld., which was found in a Chipeway Indian, is of the same species in spite of the shorter segments. *Tænia echinococcus*, v. Sieb., 1853. Syn.: _Tænia nana_, v. Ben., 1861 (_nec_ v. Sieb., 1853); _Echinococcifer echinococcus_, Weinld., 1861. _Tænia echinococcus_ measures 2·5 to 5 or 6 mm. in length; the head is 0·3 mm. in breadth, and has a double row of twenty-eight to fifty hooklets (on an average thirty-six to thirty-eight) on the rostellum. The size and form of these hooklets vary (the larger ones are 0·040 to 0·045 mm. in length, the smaller ones are 0·030 to 0·038 mm. in length). The suckers measure 0·13 mm. in diameter; the neck is short; there are only three or four segments, the posterior segment being about 2 mm. in length and 0·5 mm. in breadth. The genital pores alternate; there are forty to fifty testicles; the vas deferens is spirally coiled; the cirrus pouch is pyriform. The ovary is horseshoe-shaped with the concavity directed backwards; the vitellarium double, each half almost bean-shaped, at right angles to the plane of the segment; the shell gland is round. The median trunk of the uterus is dilated when filled with eggs and (instead of lateral branches) has lateral diverticula. It is not unusual for the eggs to form local heaps. The embryonal shell (embryophore) is moderately thin, with radial striæ, almost globular, 30 µ to 36 µ in diameter. [Illustration: FIG. 250.--_Tænia echinococcus_: the cirrus sac, the vagina, uterus, ovary, shell gland and vitellarium, and the testicles at the sides are recognizable in the second proglottis; the posterior proglottis shows the uterus partly filled with eggs, as well as the cirrus sac and the vagina. 50/1.] When mature this parasite lives in the small intestine of the domestic dog, the jackal, and the wolf, and apparently also in _Felis concolor_, and is usually present in great numbers; it can also be transmitted experimentally to the domestic cat, one successful result out of seven (Dévé).[292] The larval stage (_Echinococcus polymorphus_) lives in various organs--chiefly in the liver and lungs--of numerous species of mammals (twenty-seven), especially in sheep, ox and pig, and it is even not uncommon in man, though the Tænia itself has never been found in a human being; accordingly man can only acquire the echinococcus by ingesting the eggs of the “dog worm.” The dogs disseminate the eggs of _Tænia echinococcus_ wherever they go, or carry them to their mouths and coats by biting up the evacuated segments, and are thus able to transmit them directly to human beings (by licking them or making use of the same crockery, etc.). In other cases the oncospheres, enclosed in the embryophores, must withstand desiccation for a time and then (as when the dogs are “kissed” or otherwise caressed) are transmitted into or on to man. As echinococcus disease in man is always very dangerous, it would be a matter of general interest to prevent dogs being infected by destroying the echinococci,[293] and all measures would be justifiable which would diminish the superfluous number of house-dogs (for instance, high taxes); measures should also be adopted to limit the association of men with dogs, particularly in such frequented places as restaurants, railway carriages and tram-cars. [292] In Iceland 28 per cent. of the dogs are infected with this Tænia, in Lyons 7·1 per cent., in Zurich 3·9 per cent., in Berlin 1 per cent., and in Copenhagen 0·4 per cent. In Australia even 40 to 50 per cent. of the dogs are affected. It is, however, a question whether, in addition to _Tænia echinococcus_, a second analogous form is not involved, as the form from _Canis dingo_ attains a length of 10 to 30 mm. [293] Mosler, F., “Ueb. Mittel z. Bekampfg. endem. vork. Echinococcuskrank.,” _Deutsch. med. Zeit._, 1889, No. 72. Echinococcus is very common in slaughtered animals; in Germany, however, the figures in the reports of the abattoirs present an erroneous view in so far as, besides the total number of animals slaughtered, only the numbers of those organs (liver and lungs) are published that were so severely infected with echinococci that, even when the parasites were “shelled” out, the flesh could not be placed upon the market and was therefore “condemned.” In Berlin the following animals were slaughtered:-- -------+---------+---------+---------+---------+---------+--------- Year | 1889–90 | 1890–91 | 1891–92 | 1892–93 | 1896–97 | 1902 -------+---------+---------+---------+---------+---------+--------- Oxen | 154,218 | 124,593 | 136,368 | 142,874 | 146,612 | 153,748 Sheep | 430,362 | 371,943 | 367,933 | 355,949 | 395,769 | 434,155 Pigs | 442,115 | 472,859 | 530,551 | 518,073 | 694,170 | 778,538 -------+---------+---------+---------+---------+---------+--------- During the same years the following were condemned in consequence of being infected with echinococci:-- -----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+----- |Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver|Lung |Liver -----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+----- Oxen |7,266|2,418|5,792|1,938|4,497|1,721|2,563| 739|3,284|1,156| 2,507| 791 Sheep|5,479|2,742|4,595|2,059|4,435|1,669|3,331|1,161|4,561|1,939|11,138|4,437 Pigs |6,523|5,078|5,083|3,735|6,037|4,374|6,785|4,312|7,888|5,398| 9,544|9,233 -----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+----- Nevertheless there are statistics that give the total number of animals infected with echinococcus:-- --------+-------------+--------------+--------------+-------------- Author | Place | Oxen | Sheep | Pigs --------+-------------+--------------+--------------+-------------- Längrich|Rostock i. M.|26·2 per cent.|37·0 per cent.| 5·4 per cent. Olt |Stettin | 7·1 " |25·8 " | 7·3 " Steuding|Gotha |24·6 " |35·4 " |21·4 " Prettner|Prague |23·2 " | 5·5 " | ? --------+-------------+--------------+--------------+-------------- In Güstrow, in Mecklenburg, half of the animals slaughtered are said to be infected with echinococcus; in Wismar 25 per cent. of the oxen, 15 per cent. of the sheep and 5 per cent. of the pigs are infected; according to Mayer, in Leipzig, 3·79 per cent. native pigs, 24·47 per cent. Hungarian pigs, and 13·09 per cent. of sheep were infected with echinococcus; at the same time it was stated that in regard to the native pigs the liver was more frequently affected than the lungs (3·81 per cent. as compared with 0·26 per cent.); in sheep the lungs were more frequently infected (12·71 per cent. to 3·73 per cent.), whereas in the Hungarian pigs both organs were almost equally infected (14·78 per cent. to 12·03 per cent.). The data of Lichtenheld, in Leipzig, give the frequency with which various organs were affected, as shown in the following table:-- -----------+---------+-------------------+---------+--------- | Cattle | Pigs | Sheep | Horses -----------+---------+-------------------+---------+--------- | | ♂ | ♀ | | |per cent.|per cent.|per cent.|per cent.|per cent. Lungs | 69·3 | 16·2 | 21·4 | 52·2 | 5·5 Liver | 27·0 | 74·2 | 72·0 | 44·9 | 94·5 Spleen | 2·2 | 3·2 | 2·7 | 2·9 | -- Heart | 0·75 | 3·2 | 1·3 | -- | -- Kidneys | 0·75 | 3·2 | 1·3 | -- | -- Sub- | | | | | peritoneal| | | | | tissue | -- | -- | 1·3 | -- | -- -----------+---------+---------+---------+---------+--------- STRUCTURE AND DEVELOPMENT OF ECHINOCOCCUS (HYDATID). [Illustration: FIG. 251.--_Echinococcus veterinorum_: the fibrous sac enclosing the echinococcus has been opened and laid back in five parts, so that the surface of the bladder worm may be seen, with the brood capsules, visible to the naked eye, showing through it. Natural size. (After Leuckart.)] An echinococcus is a spherical or roundish bladder full of a watery liquid, which originates by liquefaction of the oncosphere, and in man may attain the size of a child’s head, but remains smaller in cattle (the size of an orange or apple). The thin wall of the bladder is composed of an external laminated cuticle (ectocyst) and an internal germinal or parenchymatous layer (endocyst). The latter again exhibits two layers: an outer layer of small cells that are less sharply defined, and an inner layer of larger cells. It contains, in addition, calcareous corpuscles, muscular fibres and excretory vessels. It is rich in glycogen. [Illustration: FIG. 252. FIGS. 252 and 252A.--Diagrams of mode of formation of brood capsule and scolices. (1) Wall of mother cyst, consisting of ectocyst and endocyst; (2) theoretical stage of invagination of wall; (3) a brood capsule with the layers of the wall in the reverse position to that in the mother cyst; (4) evagination of wall; (5) invagination; (6) fusion to form the solid scolex; (7) invagination of fore-part of scolex into hind-part. (_Note._--The size of the scolex is much out of proportion to the brood capsule.) (Stephens.)] The development in cattle often remains stationary at the bladder stage, and they are then called “acephalocysts,” or _Echinococcus cysticus sterilis_. According to Lichtenheld, sterile cysts occur in 80 per cent. of cases in cattle, in 20 per cent. in pigs, and in 7·5 per cent. in sheep. In other cases large numbers of small, hollow BROOD CAPSULES are formed in the germ layer, but are not arranged in any particular order. The order of the layers is just the reverse in them to what it is in the parent cyst, that is to say, they have inside a thin non-laminated cuticle and the parenchymatous layer on their external surface. These, theoretically at least, may be regarded as invaginations of the bladder wall giving rise to a cavity with the cuticle internal and the parenchymatous layer external. If we suppose the orifice to close, we should then get an isolated cavity with cuticle internal and parenchymatous layer external, as in the brood capsule (fig. 252). If we next suppose an evagination of the wall of the brood capsule to occur at one point we should get a hollow process _lined_ with cuticle; at the bottom of this we get the scolex and hooklets formed, and a little higher up the tube the suckers (fig. 252, 4). If this hollow scolex is now pictured as being invaginated we get a hollow scolex _covered_ with cuticle and lined by a parenchymatous layer projecting into the cavity of the brood capsule. The two sides of this hollow scolex now fuse and we get a solid scolex projecting into the cavity. Finally, if we imagine once more the rostellum and suckers invaginated into the posterior part of the scolex we get the condition as frequently found in the brood capsules, _i.e._, a scolex covered with cuticle projecting into the cavity, with the rostellum and suckers invaginated into the posterior portion of the scolex (fig. 252A, 7). [Illustration: FIG. 252A.] A large hydatid may contain many thousands of brood capsules. Each brood capsule is about as big as a pin’s head, and may contain ten to thirty or more scolices. The delicate wall of the brood capsules may rupture, so that the scolices are now free in the mother cyst. These free scolices and also free brood capsules constitute what is known as “hydatid sand,” which settles at the bottom of a glass when hydatid fluid is poured into it. This form occurs chiefly in domesticated animals and is termed _E. veterinorum_, Rud., or _E. cysticus fertilis_. In man, and only rarely in cattle, the mother cyst first forms “daughter cysts” (_E. hominis_, Rud. [fig. 255]), which, though smaller than the “mother cyst,” resemble it in the structure of their walls; thus they are covered externally by a laminated cuticle and internally by the parenchymatous layer. They originate: [Illustration: FIG. 253.--Section through an invaginated echinococcus scolex. _Cf._ fig. 252A, 7. × 300. (After Dévé.)] [Illustration: FIG. 254.--A piece of the wall of an _Echinococcus veterinorum_ stretched out and seen from the internal surface. A few brood capsules (the outline of which is only faintly shown), with scolices directed towards their interior and exterior. 50/1.] (1) Between the laminæ of the cuticle of the mother cyst from small, detached portions of the parenchymatous layer; during their growth they bulge inwardly or outwardly and may separate themselves entirely from their parent cyst. In the latter case they lie between the mother cyst and the capsule of connective tissue formed by the host (_E. granulosus_ or _E. hydatidosus exogenus_); when growing inwardly they reach the interior of the mother cyst (_E. hydatidosus endogenus_). Their number is very variable and does not depend on the size of the mother cyst. They are as big as, or bigger than, gooseberries. (2) According to some authors, endogenous daughter cysts arise also from a _metamorphosis of scolices_ that have separated off from the brood capsule. This takes place in the following way: Fluid accumulates in the interior of the scolex, so that eventually nothing remains except a sac consisting of cuticle lined by parenchyma. The cuticle gradually thickens and several layers form (fig. 257). [Illustration: FIG. 255.--_Echinococcus hominis_ in the liver. The fibrous capsule and the wall of the echinococcus have been incised, so that the endogenous daughter cysts may be seen. Reduced. (After Ostertag, from Thoma.)] [Illustration: FIG. 256.--Section through an echinococcus scolex in process of vesicular metamorphosis, twenty-six days after insertion in the pleural cavity. × 250. (After Dévé.)] (3) _Transformation of Brood Capsules into Daughter Cysts._--This is also held to be possible by various observers. New epithelial layers are deposited between the cuticle which lines the brood capsule and the outer parenchymatous layer. This parenchymatous layer gradually disappears and a new parenchymatous layer forms in the interior from the parenchyma of the scolex or scolices. Although it appears strange that a completely formed scolex with specifically differentiated tissues and organs should retrogress to more primitively organized matter, and again become a proliferating bladder, yet we can hardly doubt that the older observations, regarding such a vesicular metamorphosis, of Bremser (1819), v. Siebold (1837), Naunyn (1862), Rasmusser (1866), Leuckart (1881), Alexinsky (1898), Riemann (1899), Dévé (1901), and Perroncito (1902) are correct. (4) Further, _a fourth method_ of formation of daughter cysts is described by Naunyn as occurring in sterile hydatids, _i.e._, those containing no brood capsules. In this case a portion of the mother wall of the hydatid gets constricted off. [Illustration: FIG. 257. Figs. _257_ and 257A.--Diagram of transformation of a scolex into a daughter cyst (1 to 3): 1, scolex in brood capsule; 2, liquefaction of scolex; 3, daughter cyst; and (4 to 6) of a brood capsule into a daughter cyst; 4, brood capsule with scolex; 5, deposition of new epithelial layers on the inner layer of the parenchyma; 6, disappearance of outer parenchyma and formation of inner parenchyma from the parenchyma of scolex, which has now disappeared. (_Note._--The scolices are out of proportion to the brood capsules and to the daughter cysts. Stephens.)] It has also been established that not only daughter cysts transplanted into animals develop further (Lebedeff, Andrejew, Stadnitzky, Alexinsky, Riemann), but that this also holds good if only hydatid _scolices_ from man or animals are transplanted into animals (rabbits). They develop into echinococci and can then give rise to brood capsules and scolices. As Dévé further established, hydatid _scolices_ are not capable of developing in guinea-pigs, while corresponding experiments with rabbits are in the large majority of cases successful where the scolices are introduced subcutaneously or into the pleural or peritoneal cavities. It is only in the case of _daughter cysts_ that further growth is obtained in the case of guinea-pigs. Finally it appears, as has been already stated, that brood capsules can transform themselves into daughter cysts, but according to Dévé only within the mother cyst, not after transplantation. Daughter cysts that have been formed in the mother cyst of man and animals behave themselves just as the mother cyst does, _i.e._, they can remain sterile, or give rise to brood capsules and scolices, or even again to fresh cysts--granddaughter cysts. The mother cyst can also die, so that the daughter cysts then lie in the cavity of the connective tissue capsule. The number of the daughter cysts in either case may attain several thousands. [Illustration: FIG. 257A.] The echinococcus fluid, which originally is formed from the blood of the host, is light yellow, with a neutral or slightly acid reaction; its specific gravity averages 1009 to 1015. It contains about 1·5 per cent. of inorganic salts, half of which is common salt; in addition (besides water) it contains sugar, inosite, leucine, tyrosin, succinic acid (associated with lime or soda) and albumens which are not coagulated by heat; occasionally also the fluid has been found to contain hæmatoidin and uric acid salts (in echinococcus of the kidneys), which doubtless demonstrates that the echinococcus liquid originates from the host. It has been generally assumed that echinococcus fluid contains a toxic substance the escape of which into the body cavity (at operation or by bursting of a hydatid cyst) produces more or less severe symptoms (fever, peritonitis, urticaria), so much so that one speaks of hydatid intoxication. The investigations of Kobert, Joest, etc., have, however, shown the harmlessness of fresh undecomposed hydatid and cysticercus fluid for rabbits, mice and guinea-pigs, whether inoculated intraperitoneally, subcutaneously or intravenously. Contrary data or clinical experience must accordingly depend on other factors. According to the researches of Leuckart, the growth of the echinococcus is very slow; four weeks after infection the average size is only 0·25 to 0·35 mm., at the age of eight weeks it is 1 to 2·5 mm., and at this period the formation of the central cavity commences; at the age of five months, and with a size of 15 to 20 mm., the first brood capsules with scolices are formed. The consequence of this gradual increase of size is that the organ attacked can maintain its functions by vicarious hypertrophy, and that many echinococci induce no special symptoms and cannot even be diagnosed, the latter circumstance being due to their hidden position. The echinococcus cannot be said to be scarce in man, as is shown by the following table for Central Europe:-- --------------------+-------+--------------+------------+---------- Place | | No. of |No. of cases|Percentage |Period |_post-mortems_| of echino. | --------------------+-------+--------------+------------+---------- Rostock |1861–83| 1,026 | 25 | 2·43 Greifswald |1862–93| 3,429 | 51 | 1·48 Jena |1866–87| 4,998 | 42 | 0·84 Breslau |1866–76| 5,128 | 39 | 0·761 Berlin |1859–68| 4,770 | 33 | 0·69 Würzburg | -- | 2,280 | 11 | 0·48 Göttingen | -- | 639 | 3 | 0·469 Dresden |1852–62| 1,939 | 7 | 0·36 Münich |1854–87| 14,183 | 35 | 0·25 Vienna | 1860 | 1,229 | 3 | 0·24 Prague | -- | 1,287 | 3 | 0·23 Kiel |1872–87| 3,581 | 7 | 0·19 Zürich, Basle, Berne| -- | 7,982 | 11 | 0·13 Erlangen |1862–73| 1,755 | 2 | 0·11 --------------------+-------+--------------+------------+---------- These, however, are only cases that have become known by _post-mortem_; in addition, there are cases that have been treated medically, of which there are a few statements, at all events relating to the principal districts of Germany. According to Madelung, one case of echinococcus occurs in every 1,056 inhabitants in the town of Rostock, in the district of Rostock one to every 1,283, in Schwerin one to every 5,887, and in Ludwigsort one to every 23,685; according to Peiper, in Upper Pomerania one case occurs to every 3,336, in the district of Greifswald one to every 1,535 inhabitants. The northern districts of Pomerania are more affected than the southern ones. Accordingly, echinococcus is also considerably more frequent in cattle in Pomerania. On an average in Germany 10·39 per cent. oxen, 9·83 per cent. sheep, and 6·47 per cent. pigs are infected, whereas in Upper Pomerania 37·73 per cent. oxen, 27·1 per cent. sheep, and 12·8 per cent. pigs are infected; in Greifswald, indeed, 64·58 per cent. oxen, 51·02 per cent. sheep, but only 4·93 per cent. pigs are infected. In accordance with these figures _Tænia echinococcus_ must be frequent in dogs in Pomerania, especially in Upper Pomerania; on the other hand, the conjecture that the frequency of echinococcus in Mecklenburg is explained by the occurrence of _Tænia echinococcus_ in foxes has not been confirmed, as the fox does not harbour this worm in Mecklenburg. Beyond the European continent, echinococcus is frequent in the inhabitants of Iceland, Argentine, Paraguay and Australia. In Iceland, according to Finsen, 1 in every 43 inhabitants is affected with echinococcus; according to Jonassen the proportion is 1 to 63; this is due to the habits of the people of Iceland or, in fact, to the frequency of _Tænia echinococcus_ in dogs, and the prevalence of the hydatid in cattle. In certain districts of Australia it is just as frequent. In Cape Colony, Egypt and Algeria echinococcus is not rare, but it is scarce in America and in Asia, with the exception of the nomadic tribes of Lake Baikal. [Illustration: FIG. 258.--Hooklets of echinococcus. _a_, of _Echinococcus veterinorum_; _b_, of _Tænia echinococcus_, three weeks after infection; _c_, of the adult _Tænia echinococcus_; _d_, the three forms of hooklets outlined one within the other. 600/1. (After Leuckart.)] Echinococcus attacks persons of every age, though it is rare in children up to 10 years of age and in old people. It occurs most frequently between the ages of 21 and 40 years. According to all statistics it preponderates in women (about two-thirds of the cases). The liver is its favourite seat (57·1 per cent. of the cases); next in order come the lungs (8 per cent.), kidneys (6 per cent.), cranial cavity, genitalia, organs of circulation, spleen (3·8 per cent.), etc. As a rule one organ only is invaded; multiple occurrence may originate from one infection, or eventually from a later infection (?), or it may come to pass that from some cause (through the spontaneous rupture of an echinococcus, or the rupture of one caused by an injury or surgical operation) daughter cysts, brood capsules or scolices escape into the abdominal cavity,[294] where they settle or become transformed and go on growing. In the distribution of this secondary echinococcus the great powers of motility of the free scolices must be taken into account (Sabrazès, Muratet, and Husnot). [294] In such cases the toxic effects of the echinococcus fluid usually--if not always--manifest themselves. Such effects are manifested by severe symptoms of poisoning being set up, by urticaria, peritonitis, and ascites, and not infrequently they cause a fatal termination. Human echinococci may also die at various stages of development, become caseous or calcified, or may be absorbed, the cause for this being either disease of the hydatid itself or inflammation of its connective tissue capsule; the discovery of the laminated cuticle, which has great powers of resistance, or the finding of the hooklets of the scolices is sufficient to form a conclusion as to the nature of such formations. Siebold (1853) was the first to rear _Tænia echinococcus_ in the dog by feeding it with the echinococcus of cattle and especially of sheep. Küchenmeister, van Beneden, Leuckart, Railliet and others obtained similar results, and Thomas, Naunyn, Krabbe and Finsen succeeded in rearing _T. echinococcus_ in dogs from the bladder worms of human beings; these grow comparatively slowly (one to three months[295]) and only during the process of growth develop their hooklets in their definite form (fig. 258). It lies in the nature of things that dogs, whether experimentally or naturally infected, almost always harbour _T. echinococcus_ in large quantities. That cats exceptionally harbour these worms has been already mentioned (Dévé). Finally, Leuckart infected young pigs by feeding them with mature segments. [295] According to Perroncito the scolices had not formed proglottids nine days after feeding, but the latter were present twenty-four days after feeding, although the formation of eggs had not begun. *Echinococcus multilocularis* (alveolar colloid). In addition to the form of echinococcus already described, and which is also frequently termed _Echinococcus unilocularis_, there is a second form which occurs in man as well as in animals, and which is termed _E. multilocularis_, s. _alveolaris_ (alveolar colloid). It was originally regarded as a tumour; its animal nature was first established by Zeller and R. Virchow. The parasite, which varies in size from that of a fist to a child’s head, presents a collection of numerous cysts, measuring between 0·1 and 3 to 4 mm. to 5 mm. in diameter, which are embedded at first in a soft, connective tissue stroma; the cut surface has therefore a honeycomb appearance. The cysts are surrounded by a pellucid and laminated cuticle, and each according to its size encloses either a small-celled tissue or a cavity lined by a parenchymatous layer; the fluid contained in such a cavity may be transparent, or is rendered opaque by globules of fat, bile-pigment, hæmatoidin and fat crystals. According to some authors all or most of these cysts intercommunicate; others state that this is the case at least as regards the cuticle. The scolices are by no means found in all the cysts, and when present only a few, rarely half, of the cysts contain scolices (one or more); it is supposed that at least some of these scolices are formed in brood capsules, and that the former are capable of undergoing a cystic metamorphosis. One circumstance is peculiar to the multilocular echinococcus of man, namely, the disintegration that sets in at certain stages; in the centre of the parasite a cavity forms that frequently becomes very large and is filled with a purulent or brownish or brownish-green viscid fluid; in this fluid one finds shreds of the wall of the cavity, calcareous bodies, echinococcus cysts, also scolices and hooklets, as well as fat globules and crystals of hæmatoidin, margarine and cholesterin and concretions of lime. Such ulcerative processes, according to Ostertag, are never present in the multilocular echinococcus of oxen,[296] in which the separate cysts are larger and the connective tissue integument less powerfully developed. [296] This may perhaps be explained by the fact that the hosts are slaughtered before the parasites have attained the size or other conditions necessary to disintegration. [Illustration: FIG. 259.--_Echinococcus multilocularis_ in the liver of the ox. Natural size. (After Ostertag.)] Hardly anything positive is known with regard to the development of the alveolar echinococcus; its peculiar conformation is attributed by some to enormous infection of oncospheres, by others to the abnormal situation of one oncosphere; a few authors ascribe it to infection of lymphatic vessels, others to infection of the biliary ducts or to peculiarities of the surrounding hepatic tissue; Leuckart ascribes it to a grape-like variety of form which continues budding; a few more recent authors consider multilocular echinococcus to be specifically different from unilocular echinococcus, and therefore also different the species of Tænia arising from them. Melnikow-Raswedenkow is also of this opinion. According to this author the oncospheres infect the lumen of a branch of the portal vein in Glisson’s capsule of the liver and grow into an irregularly shaped formation (chitinous coil), which breaks through the vascular walls and thus forms the alveoli. So far the data coincide well with Leuckart’s opinion of the original grape-like form of the _Echinococcus multilocularis_; according to Melnikow-Raswedenkow the “granular protoplasmic substance” (parenchymatous layer) is not only present in the interior of the loculi but also outside, and, moreover, “ovoid embryos” are supposed to develop in the chitinous coils, which, “thanks to their amœboid movements, reach the lumen of a vessel, where, under favourable circumstances, they begin to develop further,” that is to say, they become “chitinous cysts with fantastic outlines,” or also “single-chambered chitinous cysts”; scolices may develop in both. Dévé, however, considers that these embryos are only prolongations of the protoplasmic layer which secondarily cuticularize. The multilocular echinococcus, which in man produces a severe disease and almost always leads to premature death, infects most frequently the liver, but may also be found primarily in the brain, the spleen and the suprarenal capsule; from the liver by means of metastasis it may reach the most various organs, especially those of the abdomen, but also the lungs, the heart, etc. Up to 1902, 235 cases have been described and up to 1906, 265, being 70 from Russia, 56 from Bavaria, 32 from Switzerland, 30 from the Austrian Alps, 25 from Würtemberg; the remaining cases are distributed over Central Germany, Baden, Alsace, France, Upper Italy, North America. In some the origin is doubtful; in any case after Russia, the mountainous South of Europe is the principal region of distribution. As to the domesticated animals, the same parasite is found principally in the ox (according to Meyer, in Leipzig, in 7 per cent. of the oxen affected with echinococcus); it is rarer in the sheep and very scarce in the pig. It has already been mentioned above that recently the multilocular echinococcus has been stated to be specifically different from hydatid or unilocular echinococcus. To this may be added the fact that Mangold, who fed a young pig with oncospheres of a Tænia reared from the multilocular echinococcus, found two growths in the liver four months later, which he took to be _E. multilocularis_, and consequently one has to assume the existence of two different worms. The chief defender of this view, already put forward by Vogler, Mangold, and Müller, is Possett. He bases his opinions on (1) the more restricted distribution of the multilocular hydatid, the former occurring in districts where only cattle are raised, the latter where sheep-breeding is established; (2) that those engaged in looking after sheep are attacked by multilocular, whereas those looking after cattle are attacked by unilocular hydatid; (3) that among the cases of unilocular hydatid occurring in the distribution areas of multilocular hydatid no transitions between the two forms are observed; (4) on the difference in the hooks both in the hydatid as well as in the Tænia stage; the hooks of _Tænia echinococcus_ are plump, sharply curved, and have a short posterior root process the length of which is to that of the total length as 1 to 4·7, whereas on the contrary the hooks of the alveolar echinococcus are more slender, slightly bent, and have a long posterior root process (1 to 2·5); and (5) on the form of the uterus, which in the alveolar Tænia has the form of a spherically distended sac anteriorly. SERUM DIAGNOSIS OF ECHINOCOCCUS. (1) _Precipitin Reaction._--Mix equal parts of hydatid fluid (of the sheep) and serum of patient. Keep at 37° C. The reaction is not decisive as it may be given by normal sera. (2) _Complement Deviation._--Required: (1) Hydatid fluid of sheep (antigen), (2) guinea-pig complement, (3) patient’s serum, (4) red cells of sheep, (5) hæmolytic serum (of rabbit) against sheep’s red cells, (6) 0·8 per cent. salt solution. Mix the antigen + patient’s serum (heated) + complement + salt solution at 37° C. for one hour. Add red cells of sheep + hæmolytic serum. Allow to stand for half an hour at 37° C. It is imperative to make adequate control observations. An example will indicate the method. Salt solution 1·3 c.c. + patient’s serum (heated) 0·2 c.c. + hydatid fluid 0·4 c.c. + complement 0·1 c.c. of serum diluted to a quarter strength + hæmolytic serum and red cell emulsion 1 c.c. Result: no hæmolysis, _i.e._, the patient’s serum contains specific (echinococcus) antibodies. C. *NEMATHELMINTHES*. BY J. W. W. STEPHENS, M.D., B.C., D.P.H. Bilaterally symmetrical animals, without limbs and with a body cavity in which the gut or other organs float. They are generally cylindrical. Class. *NEMATODA.* Nemathelminthes with an alimentary canal. Nematodes are as a rule elongated round worms of a filiform or fusiform shape; their length varies according to the species from about 1 mm. to 40 to 80 cm. The outer surface of the body is smooth or annulated, and at certain points provided with papillæ, occasionally also with bristles and alar appendages. The anterior end carrying the oral aperture is usually rather slender, occasionally quite thin; the posterior end is pointed or rounded; the anus, as a rule, lies somewhat in front of the posterior extremity. The sexes are almost always separate, and the male can as a rule be easily distinguished from the female because the former is smaller and more slender, its posterior extremity is often spiral or incurved, or carries an alar appendage, whereas the female is larger and thicker, and its posterior extremity is straight. In the male the genitalia open into the anus; the sexual orifice of the female opens ventrally along the median line in the anterior half of the body, in the middle, or a little further back. Both sexes, moreover, have an orifice, the excretory pore, which is situated ventrally in the median line and about the level of the œsophageal nerve ring. In large species, even with the naked eye, two lighter transparent bands--the lateral lines--may be distinguished; they run along the sides of the body from the anterior to the posterior end, while two other bands, the median lines, running along the ventral and dorsal mid-lines, are less evident; in exceptional cases there are also four sub-median lines. These bands or lines are inward projections of the ectoderm, and in them lie the nerves and excretory vessels (fig. 260). Some Nematodes live free in fresh or salt water, in soil, mud or decaying vegetable matter, others parasitically in the most various organs of animals, frequently also in plants. ANATOMY OF THE NEMATODES. All the Nematodes are covered by (1) a CUTICLE, which in the small species is thin and delicate, while in the larger species it is thickened, and may consist of several layers of complicated structure. Canalicular pores do not occur. According to general opinion, which is confirmed by the history of development, the cuticle is a product of (2) the EPITHELIUM or ectoderm that had formerly existed or is still found beneath it; in young specimens and small species it is perceptible, but in older worms it frequently alters so considerably that not only do the borders of the cells disappear,[297] but a fine fibrous differentiation appears in their cytoplasm. The matrix or ectoderm then has the appearance of an ectodermal syncytium permeated by fibres and strewn with nuclei, so that it is hardly distinguishable from the tissue of (3) the CUTIS, which is always present, though developed to a varying degree. Both layers, matrix and cutis, project internally as ridges and form the lateral lines, while the less marked median lines are produced apparently only by the ectoderm (fig. 260). [297] In the _Ascaridæ_ isolated epidermal cells grow to a considerable size, and have to do with the sensory apparatus of the lips (Goldschmidt). Unicellular cutaneous glands are known in parasitic as well as in free-living species; they vary in number and arrangement, and are found discharging some at the anterior extremity and others in the vicinity of the genital orifices. In other cases large numbers of them are present along the lateral lines; they are strongly developed in most of the _Trichotrachelidæ_, where they discharge either along a part of the ventral surface or along the lateral and median lines; they are placed so closely together that the ridges of the cuticle perforated by the orifices have long been known, and have been described, as “rodlet borders,” or “fields of rods.” As the cutis is immediately adjacent to (4) the DERMO-MUSCULAR TUBE the simple layer of the muscular cells is divided into four quadrants by the longitudinal lines--two dorsal and two ventral (fig. 260). The MUSCLES are in the simplest cases large rhomboid cells that lie two by two in each quadrant, so that on transverse section of the entire worm only eight cells are perceptible. The outer border of the cells is converted into contractile fibrils, while the contiguous inner portion has remained protoplasmic, and contains the nucleus. In large species the muscular cells do not only increase in length (up to 3 mm.) and in number in every quadrant, but their contractile portion curves up to form a groove (like that of a dead leaf) thereby even becoming thicker; simultaneously space is gained for more cells, the protoplasmic parts of these cells (on transverse section) project out of the grooves like vesicles. In all cases there is only one layer of longitudinal muscular cells, which, by contracting, can shorten the body or, by contracting one side, can bend it. In the latter case the muscles of the opposite side have an antagonistic effect, or when all the muscles are contracted, the elasticity of the cuticle acts in the same way. Special muscles exist at the beginning of the gut and at sections of the genital apparatus. The existence of a cavity between the body and the gut wall has hitherto been generally assumed, and has been referred to the cleavage cavity, and consequently designated as a primary body cavity. More recent investigators, however, state that such a cavity does not exist, but that the space between the longitudinal muscles or their protoplasmic portions and the gut epithelium is filled by a complicated “isolation tissue.” This in the main proceeds from a large cell (_Is._, fig. 262) which lies directly behind the nerve ring dorsal to the œsophagus, and consists of a system of lamellæ which sheathe the muscles and penetrate through them to the cutis and also cover the gut in a thin layer. [Illustration: FIG. 260.--Diagram of a transverse section of _Ascaris lumbricoides_, showing thick cuticle, and beneath it the matrix or syncytial ectoderm. The flat intestine is in the middle, and to the right and left near it in the body wall the lateral lines with excretory vessel and lateral nerves; above and below in the centre the dorsal or ventral median lines with the nerves radiating to the muscles, also the muscle cells with their striated outer contractile portion and inner nucleated vesicular protoplasmic portion. About 50/1. (After Brandes.)] [Illustration: FIG. 261.--Anterior end of an _Ascaris megalocephala_ cut open and showing the four tuft-like organs lying on the lateral lines. Natural size. (After Nassonow.)] We may now consider the “tuft-like” or “phagocytic” organs, which attain 1 cm. in size, and consist of four, six, or even more ramified cells, which lie close to the walls of the body (fig. 261). They are found either only in the anterior part of the body (Ascaris), or throughout the whole length of the body (Strongylus, syn., Sclerostomum), and their position usually corresponds to the lateral lines. In some species there are small protoplasmic cells on the processes of these organs. In consequence of their size they can be recognized with the naked eye, especially when they are loaded with granules of stain (carmine, Indian ink) injected into the body cavity. INTESTINAL CANAL.--The oral aperture, which is situated at the tip of the anterior extremity, is frequently surrounded by thick lips, or small bristles, or papillæ; it leads to a more or less strongly developed buccal cavity, which is lined by a continuation of the body cuticle, and which in some species is provided with “teeth,” representing differentiated portions of the cuticle. THE ŒSOPHAGUS (fig. 262), which arises from the base of the oral cavity, is as a rule a short, bottle-shaped tube with triradiate lumen; its wall is chiefly composed of radiating muscular fibres, which give it the appearance of being transversely striped when viewed from the surface. There exist also in its wall three large gland cells (œsophageal glands) and nerves arising from the lateral lines and running forward. The radial fibres cause a dilatation of the lumen, and exercise an effect antagonistic to the elasticity of the cuticle lining the inner surface. The latter has its own particular layer, which is not in direct connection with that of the oral cavity. Special dilator muscles, arising from the dermo-muscular tube and situated at the commencement of the œsophagus, are only known in a few species. The posterior end of the œsophagus presents a bulb-like dilatation, and is frequently provided with small chitinous movable valves. In a few forms, which belong to the _Trichotrachelidæ_ (Trichocephalus, Trichinella), the œsophagus is a very long cuticular tube, beset on its dorsal surface with a series of large nucleated cells. In others (Cucullanus, Ascaris, etc.), a tube, the so-called glandular stomach, lined only by epithelial cells, follows behind the muscular œsophagus. This glandular stomach is, from its structure, easily distinguished from the mid-gut, or chyle intestine, which is likewise cellular. The so-called mid-gut is a tube lined by flat, cubical, or cylindrical cells (fig. 260) surrounded by “isolation tissue”; its transverse section is circular or flattened dorso-ventrally; the lumen may run in a straight line, or it runs a sinuous course through the alternating prominences of the then flat epithelial cells. The ectodermal hind gut is, as a rule, very short. At the anal opening the cuticle and the subcuticular layers are reflected inwards, forming the lining of the hind gut. In large species the subcuticular tissue forms large cells on which anteriorly lie in addition large “glandular cells.”[298] In the male the ejaculatory duct opens at this point. Around the end part of the gut, either on the chyle intestine or at the beginning of the end gut, there exists a sphincter muscle arising from a muscle cell which acts antagonistically to the two diaphragm-like dilator muscle cells which stretch from the gut to the body wall. In many species large stretches of the gut are provided with dilator muscles. There is sometimes a retrogressive absorption of the gut in the adult stage of a few parasitic species. [298] In Ankylostomes according to Looss these cells have no glandular function, but are ligaments. INTESTINAL CÆCA and ŒSOPHAGEAL GLANDS sometimes exist as intestinal appendages; the former are tubular appendages of various size, running backwards or forwards, and arising from the posterior extremity of the œsophagus. They are lacking in many species. The œsophageal glands are unicellular; a dorsal and two subventral glands may be distinguished according to their position; as a rule they open into the œsophagus at a distance from one another. The body of the gland lies in the bulb of the œsophagus, or in the dorsal _cul-de-sac_ arising from it. [Illustration: FIG. 262.--Transverse section through _Ascaris lumbricoides_ at the level of the œsophagus behind the nerve ring. _Cu._, cuticle; _Sc._, subcuticular layer; _Ex._, excretory vessel; _Is._, isolation cell and the system of lamellæ proceeding from it; _M._, muscles; _Ml._, median line; _Sl._, lateral line. Magnified. (After Goldschmidt.)] THE NERVOUS SYSTEM is sufficiently known in a few species only; it consists of a ring containing fifty to sixty fibres closely surrounding the œsophagus, various groups of ganglion cells, and a certain number of nerves extending anteriorly as well as posteriorly. The remarkably small number of fibres, as well as ganglion cells, is characteristic of the nervous system of all Nematodes. Immediately behind the œsophageal ring (fig. 263, _Lg._) an agglomeration of ganglion cells lies at either side (lateral ganglia); part of their off-shoots form the œsophageal ring, and part are directed posteriorly and ventrally, and unite partly in front of and partly at the back of the excretory pore, with fibres originating direct from the œsophageal ring, and passing along the ventral median line to the back; these fibres then together form the ventral median nerve (fig. 263, _V.m.n._). This nerve, originally consisting of thirty to fifty fibres, becomes in the female attenuated quite evenly in its further course. There is also an agglomeration of ganglion cells close in front of the anus (anal ganglia), and then the median nerve divides in order to combine with the lateral nerves on either side. In the male the median nerve enlarges to nearly the original number of fibres in front of the anal ganglion, which contains seven cells; there is also an anal ring embracing the terminal gut, and there are two ganglion cells in it on each side. In the dorsal median line the dorsal median nerve is alike in both sexes; arising in front with a single root from the œsophageal ring, it gathers its fibres from the lateral ganglia; in the anterior part of the body it consists of thirteen to twenty fibres; in the posterior part of the body the fibres are reduced to four or six; behind the anus it divides and combines with the lateral nerves; the latter consists of two fascicles at either side right up to their most posterior extent--one dorsal and one ventral--which in the greater part of the body do not run in, but beside the lateral lines, and exhibit a different origin anteriorly. The ventral fascicle at each side branches off from the ventral median nerve in front of the excretory pore, whereas the dorsal fascicles originate from the œsophageal ring close to the lateral ganglia. Each of the four fascicles contains only two or three fibres, which run backwards parallel to the lateral lines; a few centimetres in front of the caudal extremity they enter the lateral lines and remain separate from one another up to the level of the anal ganglion; here they amalgamate on either side, after each interpolating one ganglion cell, with the single short lateral nerve which first takes up the forked ends of the ventral and then of the dorsal median nerve; finally, both lateral nerves unite with each other at the back in an arch-like manner. [Illustration: FIG. 263.--Schematic representation of the nervous system of a male _Ascaris megalocephala_. _A._, anus; _Ag._, anal ganglion; _C._, commissures; _D.m.n._, dorsal median nerve; _Exp._, excretory pore; _Pr._, œsophageal sensory ring; _Lg._, lateral ganglia; _Ln._, lateral nerve; _Sp._, papilla; _V.m.n._, ventral median nerve. (After Brandes.)] In the male each ventral part of the lateral nerves becomes thickened by taking up fibres from the ventral nerves, which become thickened posteriorly to the nervus bursalis, which towards the middle gives off a mass of fibres to the “genital papillæ” situated in front of and behind the anus; the number of these fibres averages eighty to 100; in its further course the bursal nerve resembles the corresponding ventral part of the lateral nerves of the female. The ventral and dorsal nerves are connected by a number of semicircular commissures, which originate from the ventral nerves and serve to supply the dorsal nerve, which is always being decreased by fibres departing from it. It is remarkable that these commissures are not placed symmetrically, and their position also is different in the two sexes; in the female there are thirty-one on the right side and only thirteen on the left side. In the male there are thirty-three commissures on the right side and fourteen on the left, which run into the subcuticular layer, generally in pairs, and usually cross at the level of the lateral lines. The fibres of the two median nerves are chiefly motor; fascicular processes run from each protoplasmic part of the muscular cells to the median nerves; from these they take up bundles of primitive fibrils, which separate, pass through the protoplasmic part and enter the contractile part (fig. 260). One part of the fibrils, however, penetrates beyond the muscles into the subcuticular layer, where they form a network, probably of a sensory nature, with contiguous fibrils. Nerves directed anteriorly finally originate from the œsophageal ring; they consist each of three fibres, carry three ganglion cells at their point of origin, and enter the sensory organs of the three papillæ surrounding the oral aperture. Two of these little trunks lie in the lateral lines, the remaining four are situated in the middle of the four quadrants (Nn. sub-mediani anteriores). Parasitic species lack higher ORGANS OF SENSE; free-living worms occasionally have two rust-red eyes, sometimes with lenses, at the anterior part of the body. In addition to the above-mentioned sensory papillæ surrounding the oral aperture and the genital papillæ of the male at the end of the body, another pair exist in the vicinity of the lateral ganglia, the “cervical papillæ,” and two dorsal papillæ in the central region of the body and two lateral ones near the tip of the tail (_Ascaridæ_). The differences in the distribution and number of the sensory papillæ serve for characterizing the larger and smaller groups of Nematodes. THE EXCRETORY ORGANS of the Nematodes are variable. In a great many cases the apparatus is symmetrical, and consists of a vessel commencing in the posterior extremity in each lateral line (fig. 260), and passing anteriorly. In the vicinity of the anterior extremity both tubes pass out of the lateral lines, bend ventrally, and, in the median ventral line, unite into a short vesicle formed by an ectodermal cell--the cavity of which is lined by a continuation of the cuticle of the body--which opens into the excretory pore (fig. 263, _Exp._). Asymmetry is occasioned through the excretory duct proceeding from the ventral pore to the lateral line, and it here proceeds as (or takes up) the left excretory canal, which anteriorly is a broader tube and runs along the left lateral line; shortly before its union with the excretory duct it throws out a branch to the right towards the lateral line, which, however, always remains weak, and runs posteriorly in the right lateral line; a few smaller branches in addition spring from the left main stem. In other species the right branch is completely suppressed; the entire organ thus lies in the left lateral line, and consists of the excretory duct, which occasionally opens quite in front near the lips, as well as the excretory canal, which throws out a number of lateral branches. This excretory vesicle is a single elongated or horse-shoe-shaped cell, with a large nucleus and an intracellular tubular system, which is connected with the excretory duct arising from the excretory pore on the outer surface (fig. 326). The so-called ventral gland is the only excretory organ of marine Nematodes, and probably represents a primitive form. Goldschmidt, who has investigated the excretory apparatus of _Ascaris lumbricoides_, considers that the vessels running in the lateral lines are only ducts to which belong a glandular system hitherto overlooked or otherwise interpreted. This system also lies in the lateral lines, and takes the form of two glandular tracts, forming a syncytial tissue in which lie the ducts, one dorsal, one ventral. In parts these tracts are connected by commissures, although their junction with the excretory vessels cannot be clearly made out. These statements, however, require confirmation. The author has further found that the anterior ends of the lateral canals, directly before they bend ventrally, anastomose with one another and give off anteriorly a small blind process, which can be interpreted as a rudiment of a canal coming from the head end, and as a matter of fact, according to Golowin, such anterior excretory canals exist in a number of genera. In a number of Nematodes (Cheiracanthus, Capillaria, Trichocephalus, Trichinella, etc.), however, special excretory organs are lacking; possibly the cutaneous glands, which are in these species generally powerfully developed, replace these organs. SEXUAL ORGANS.--With the exception of a few species, the Nematodes are sexually differentiated. (_a_) _Female Sexual Organs._--The sexual orifice (vulva), surrounded by thick labia, is, as a rule, ventral and varies in position from near the head to near the anus. It leads into a short or long vagina (ectodermic), bifurcating into the two uteri, which may be long or short; the long filiform ovaries are continuations of them (fig. 264). Further there is often, _e.g._, in Ankylostoma, a differentiation into the following parts: (1) _Ovejector_: the specialized portion of the uterus before it joins the vagina; there may be a separate one for each uterus, or a common one for both uteri. (2) _Seminal receptacle_: at the other extremity of the uterus. (3) _Oviduct_: a narrow tube connecting the ovary with the uterus proper. (For the explanation of the terms _convergent_ and _divergent_ uteri _vide_ footnote p. 432.) Uterus and ovaries, which arise in the first place from a single cell, lie between the body wall and the gut and are surrounded by connective tissue. In some species (for instance, Trichinella) the ovary is single. [Illustration: FIG. 264.--Diagram of female genitalia. _Ov._, ovary (in part); _Ovd._, oviduct; _Rec. sem._, seminal receptacle; _Ut._, uterus (in part); _Ovj._, ovejector; _Vag._, vagina.] [Illustration: FIG. 264A.--Diagram of male genitalia of a strongylid. _Test._, testis (in part); _S.V._, seminal vesicle; _c.g._, cement gland surrounding ejaculatory duct; _sp._, spicules; _cl._, cloaca; _gub._, gubernaculum; _p.p.a._, pulvillus post-analis; _g.c._, genital cone; _l.d._, dorsal lateral line; _l.v._, ventral lateral line (the bursa is not shown).] [Illustration: FIG. 265.--Transverse section through the ovarian tube of _Belascaris cati_ of the cat at various levels. To demonstrate the development (right to left) of the ova and of the rhachis. Magnified.] At the blind end of the ovary there is a mass of protoplasm with numerous nuclei that multiply continuously. Gradually the nuclei arrange themselves in longitudinal rows (fig. 265) and the protoplasm commences to leave the periphery and surround each nucleus. The nearer to the uterus the more progressive is this loosening process, until club-shaped cells each containing a nucleus are developed. The most pointed end of each, however, is still attached to an axial fibre of protoplasm, the _rhachis_; probably this has some connection with the nutrition of the ova. Finally the ova fall off and reach the uterus, where they are fertilized and enclosed in shells. (_b_) _Male Sexual Organs._--There is never more than one testis (fig. 266), which is a straight or sinuous tube of the same construction as an ovary, and in which the mother cells originate in the same manner as the ova. In the same way as the ovary passes into the uterus, so does the testis pass into the spermatic duct; the latter is often divided into the somewhat dilated seminal vesicle and into the muscular ductus ejaculatorius, which, running ventral to the intestine backward (fig. 267), finally opens into the cloaca. In many species, _e.g._, _A. duodenale_, the ejaculatory duct is surrounded for a greater or less portion of its extent by the cement gland, the secretion of which (brownish or blackish in colour) serves for copulation. The ejaculatory duct of the large _Ascaridæ_ is for the most of its course surrounded by a muscular network which takes its origin from the two dilator cells of the gut (fig. 268 _F_.). The spermatozoa of the Nematodes, it may be noted, only attain their full development after the sperm mother cells have been conveyed by copulation into the uteri of the female genitalia. In their form (sheathless, capable of amœboid motion) they differ from those of most other animals. SPICULES.--The male genital apparatus is also provided with one or two sacs, situated on the dorsal side of the intestine, and opening into the cloaca. In each sac there is a chitinous rod-like body, the spicule. Further, in many cases there exists, more or less fixed in the dorsal wall of the cloaca, a chitinous structure, the accessory piece or _gubernaculum_, the latter name implying its function of guiding the spicules during copulation (fig. 264A). A special muscular apparatus, consisting of protractors and retractors, moves the spicules. The protractors or exsertors in the large Ascaridæ consist of four flat band-like muscles which surround the spicule sac. Two long muscle cells which arise proportionally far forward on the dorsal side of the lateral line and are inserted into the base of the spicules serve as retractors. The spicules can be projected from the cloacal orifice (anus) during copulation, and when they are introduced into the vagina they serve as prehensile organs, perhaps also as stimulatory organs. [Illustration: FIG. 266.--Male of the rhabditic form of _Angiostomum nigrovenosum_. _A._, anus; _I._, mid-gut; _T._, testicular tube; _O._, oral orifice; _P._, papillæ; _Sp._, spicule. Magnified.] [Illustration: FIG. 267.--Transverse section through the posterior extremity of the body of _Ascaris lumbricoides_ (male). The intestine is in the middle, and the lateral lines are subjoined thereto; above the intestine the two spicule sacs are seen; below is the ductus ejaculatorius. The muscular fibres are between the lateral and median lines. Magnified.] BURSA COPULATRIX.--The males in many genera possess epidermal wing-like appendages at their posterior extremity. These are supported by elongated tactile papillæ called ribs. In the most highly developed bursæ, _e.g._, in the _Strongylidæ_, the ribs are called rays, as they consist not only of nerve fibres but mainly of “pulp,” _i.e._, prolongations of the subcuticular layer. Bursæ are either open, _i.e._, bilaterally symmetrical, or closed, when the posterior border is continuous all round. A _pseudo-bursa_ is one unsupported by ribs or rays, _e.g._, in Trichuris. The bursa serves as an organ of prehension during copulation. Some forms, moreover, carry a sucker at the posterior extremity (_e.g._, Heterakis); in others the spicules and other prehensile organs are absent; they are then replaced by an evertible cloaca, _e.g._, Trichinella. DEVELOPMENT OF THE NEMATODES. After impregnation, the ovum develops around itself a delicate membrane (vitelline membrane), and subsequently an egg-shell is formed. This is derived either as a secretion from the uterine wall or it is a further differentiation of the vitelline membrane, the original single membrane splitting into two, the outer becoming the egg-shell. Further the uterus often secretes a special albuminous covering around the egg-shell. The “yolk” granules of the ovum are secretions of the protoplasm of the ovum itself and first appear when the rhachis is formed. In certain cases ova lie in follicles or capsules formed of epithelium cells derived from the ovarian tubes. These cells subsequently fuse and form a membrane--the CHORION. [Illustration: FIG. 268.--Hind end of a male _Ascaris lumbricoides_ cut across at the level of the dilator cells of the gut. _D._, gut; _Dil._, dilator cells of the gut; _F._, a process of the dilator cells forming a network over the vas deferens; _Sl._, lateral line; _Sp._, spicule; _Vd._, vas deferens. The anterior end of the worm lies to the right. Magnified. (After Goldschmidt.)] The shape of the completed eggs is characteristic of the different species, and therefore a single egg often suffices to diagnose the species. According to the species, the eggs may be deposited sooner or later, either before or during segmentation, or with the embryo perfectly developed. Only a few species are viviparous, _e.g._, _Dracunculus mediensis_, _Trichinella spiralis_; in the other Nematodes the further development of the extruded eggs takes place after various lengths of time in the open, in moist earth, or in water. Thick-shelled eggs can maintain their developmental capacity for a long time, even after prolonged desiccation. Finally, a nematode-like embryo develops, which usually lies somewhat coiled up within the shell, and varies in its further development according to the species to which it belongs. In the simplest forms, as in the free-living Nematodes, the embryos, apart from their size, resemble their parents, and grow up into these after leaving the egg-shell. In many parasitical Nematodes, however, the young must be called _larvæ_, as they present characters which are subsequently lost. The manner of conveyance of the eggs or the embryos contained in them after they have left the body into the definite host is very different in the various species. (1) _Without Intermediate Host._--(_a_) In many the conveyance into the definite host is effected directly after the larvæ have developed within the eggs; thus, for instance, the feeding of suitable animals with the embryo-containing eggs of species of Trichocephalus and Ascaris leads to an infection of the gut, for the young Trichocephali or Ascarides only leave the egg-shell when they have attained the intestine of the final host, in which they become adult. In other cases (_b_) Ancylostoma, Necator, the larvæ hatch in the open, and live for a time free, changing their form; they grow, cast their skin, and finally gain the intestine of the host by means of water or through the skin, when they lose their larval characters and assume the structure of the adult worm. (_c_) In a number of Nematodes, however, HETEROGONY occurs. This terms signifies a mode of development in which two structurally different sexual generations of the same species alternate with each other. To these appertains, for instance, _Angiostomum_ (syn.: _Rhabdonema_) _nigrovenosum_, which lives in the lungs of frogs and toads; this Nematode measures about 1 cm. in length and is hermaphrodite (protandric). The eggs are deposited in the pulmonary cavity, and through the cilia of the same reach the oral cavity, where they are swallowed and thus conveyed into the intestine. They pass through the entire gut, and are finally evacuated with the fæces; often, indeed, the young themselves emerge from the egg-shell within the hind-gut of the frogs. These young forms become sexually differentiated, remain much smaller than the parent, their œsophagus is differently constructed (rhabditis form), and they are non-parasitic (fig. 266). After having grown in the open they copulate; the males die soon after copulation, and the females in their own bodies develop a few young, which, given the opportunity to get into frogs, infect them, and are transformed into the hermaphroditic Angiostomum. The same manner of development occurs in other species of the same genus, and also in the case of _Strongyloides stercoralis_. (2) _With Intermediate Host._--(_a_) Frequently, however, the larvæ of Nematodes make use of one or even two intermediate hosts; their condition then resembles that of Cestodes or Trematodes, excepting that there is never a multiplication within the intermediate hosts. The larvæ become encapsuled amongst the tissues of the intermediate host, and wait till they are introduced with the latter into the final host. For instance, _Ollulanus tricuspis_, the adult form of which is found in cats, previously lives encysted in the muscular system of mice. _Cucullanus elegans_, which attains the adult stage in fishes (perch, etc.), is found encysted in species of Cyclops. Other examples of species that require an intermediate host are _Filaria bancrofti_ and _Dracunculus medinensis_. [Illustration: FIG. 269.--A piece of the trunk muscle of the pig with encapsuled embryonic Trichinæ. Magnified.] Peculiar conditions prevail in the case of (_b_) _Trichinella spiralis_. This species, which in its adult state lives in the intestine of man and of various mammals, is viviparous; the young Trichinæ, however, do not leave the intestine, but reach the intestinal wall (Cerfontaine, Askanazy) in the following way: the female intestinal Trichinæ bore into the intestinal wall, where they are found in the submucosa, or in the lumen of the dilated lacteal vessels. Here the young are born, in the intestinal wall, and leave this position with the lymph stream. Some of them, no doubt, actively bore through the intestinal wall, reaching the lymph or blood-stream, or even pass into the body cavity. What occurs during their further migrations is difficult to say at present. It has hitherto been maintained that the wandering is entirely active; for instance, the ligaturing of an artery would be no protection against the part of the body supplied by such artery being invaded by Trichinella. This observation cannot be otherwise explained than by the active progress of the young Trichinella. The question, however, may be mooted as to where and when the worms quit the blood-vessels, which they for the most part reach through the thoracic duct, the natural connection between the vascular system and the lymphatic system, to wander further independently, and ultimately reach the muscular system, in which they become encysted (fig. 269). Thus the progeny does not leave the body of the host inhabited by the parents, as is generally the case amongst helminthes, but uses it as an intermediate carrier to reach another host, which is then the final host. The latter may belong to another species, or may be another individual of the same species. This second migration is, of course, purely passive. CLASSIFICATION OF THE NEMATODA. The Nematodes are usually divided into a number of families, some of which it is at present impossible to define accurately; moreover, the definition of many genera is also in an unsatisfactory state. Family. *Anguillulidæ*, Gervais and van Beneden, 1859. A “family” name not definable. They comprise a vast number of small forms, most of which live free in fresh water, in soil, or in macerating substances; amongst them there are some which live parasitically on plants, more rarely on animals. They do not exceed 8 mm. in length. The large majority are only 1 to 2 mm., or even 0·5 mm. The uterus is straight. Eggs in the uterus at one time, one to four. Genera very numerous, but many of them insufficiently defined (Anguillula, Anguillulina, Rhabditis, Heterodera, etc.). Family. *Angiostomidæ*, Braun, 1895. Small Nematodes undefined morphologically, but characterized by heterogony, _i.e._, there is a free-living “rhabditic” generation and a parasitic “filariform” generation which succeed one another (_e.g._, Angiostomum, Strongyloides, Probstmayria). Family. *Gnathostomidæ.* Cuticle covered totally or partly with cuticular laminæ fringed posteriorly with multiple points. Head subglobular, covered with simple spines. Two spicules. Vulva behind middle of body, parasitic in vertebrates, especially mammals (_e.g._, Gnathostoma, Tanqua, Rictularia). Family. *Dracunculidæ*, Leiper, 1912. Males very small in proportion to females. Anus absent. Vulva absent (?). Genera: Dracunculus, Icthyonema (in body cavity of eel and other fish). Family. *Filariidæ*, Claus, 1885. Long thread-like Nematodes. Anus present. Œsophagus without bulb. Vulva usually in anterior half of body. Two ovaries. Generally ovoviviparous. Development often requires an intermediate host. This family is at present ill-defined, but has been already subdivided into several sub-families, _Filariinæ_, _Onchocercinæ_, _Arduenninæ_. Family. *Trichinellidæ*, Stiles and Crane, 1910. Œsophagus consisting of a chain of single cells, the lumen of the œsophagus passing through their centre. Ovary single. Vulva at junction of anterior and posterior portions. Sub-families: (1) _Trichurinæ_, (2) _Trichinellinæ_. Family. *Dioctophymidæ.* Body anteriorly armed with spines or unarmed; mouth without lips, with six, twelve, or eighteen papillæ in one or two circles; œsophagus very long without a bulb; anus terminal in female; one ovary; vagina very long; spicule in male very long; bursa cup-shaped without rays (Dioctophyme, Hystrichis, Eustrongylides). Family. *Strongylidæ*, Cobbold, 1864. Bursa, supported by rays, always present. Oviparous. Family. *Physalopteridæ.* Mouth with two large lips. Bursa with supporting papillæ in form of a lanceolate cuticular expansion, with genus Physaloptera. Family. *Ascaridæ*, Cobbold, 1864. Rather thick Nematodes. Mouth with three lips--one dorsal, two latero-ventral. Sub-families: (1) _Ascarinæ_, (2) _Heterakinæ_, etc. Family. *Oxyuridæ.* Smallish forms, 4 to 45 mm., with cuticle thickened on each side for the whole length of body in the form of a lateral flange or wing. Œsophagus long with a well-marked bulb containing a valvular apparatus. Tail end of female drawn out into a long point. Eggs asymmetrical. Males very small (about 2 mm.). One spicule. Genera: Oxyuris, Passalurus, Ozolaimus, Atractis, etc. _Mermithidæ_, greatly elongated “Nematodes,” which, in the larval stage, are parasitic in insects, but in their adult condition are free living. Cuticle with diagonal striation. Without an open mouth or anus. Oral papillæ present. Characteristic eggs with two processes, ending in a tuft of filaments. Larvæ with a movable boring spine at the head end. _Gordiidæ._--Long, thread-like “Nematodes.” Mouth and anterior portion of gut atrophied in adult. Oral papillæ absent. THE NEMATODES OBSERVED IN MAN. Family Sub-family Genus Species _Anguillulidæ_ -- _Rhabditis_ _R. pellio._ _R. niellyi._ _Rhabditis sp._ _Anguillula_ _A. aceti._ _Anguillulina_ _A. putrefaciens._ _Angiostomidæ_ -- _Strongyloides_ _St. stercoralis._ _Gnathostomidæ_ -- _Gnathostoma_ _Gn. siamense._ _Gn. spinigerum._ _Dracunculidæ_ -- _Dracunculus_ _D. medinensis._ _Filariidæ_ _Filariinæ_ _Filaria_ _F. bancrofti._ _F. demarquayi._ _F. taniguchi._ _F. (?) conjunctivæ._ Group. _Agamofilaria_ -- _Ag. georgiana._ _Ag. palpebralis._ _Ag. oculi humani._ _Ag. labialis._ _F. (?) romanorum- orientalis._ _F. (?) kilimaræ._ _F. (?) sp. ?_ (_Mikrofilaria_) _Mf. powelli._ _Mf. philippinensis._ _Setaria_ _S. equina._ _Loa_ _L. loa._ _Acanthocheilonema_ _Ac. perstans._ _Dirofilaria_ _Di. magalhãesi._ _Onchocercinæ_ _Onchocerca_ _O. volvulus._ _Trichinellidæ_ _Trichurinæ_ _Trichuris_ _T. trichiura._ _Trichinellinæ_ _Trichinella_ _T. spiralis._ _Dioctophymidæ_ -- _Dioctophyme_ _D. gigas._ _Strongylidæ_ _Metastrongylinæ_ _Metastrongylus_ _M. apri._ _Trichostrongylinæ_ _Trichostrongylus_ _T. instabilis._ _T. probolurus._ _T. vitrinus._ _Hæmonchus_ _H. contortus._ _Mecistocirrus_ (_Nematodirus_) _M. fordi._ _Ancylostominæ_ Group. _Œsophagostomeæ_ _Ternidens_ _T. deminutus._ _Œsophagostomum_ _Œ. brumpti._ _Œ. stephanostomum_ var. _thomasi_. _Œ. apiostomum._ Group. _Ancylostomeæ_ _Ancylostoma_ _A. duodenale._ _A. ceylanicum._ _A. braziliense._ Group. _Bunostomeæ_ _Necator_ _N. americanus._ _N. exilidens._ Group. _Syngameæ_ _Syngamus_ _S. kingi. Physalopteridæ_ -- _Physaloptera_ _P. caucasica._ _P. mordens._ _Ascaridæ_ _Ascarinæ_ _Ascaris_ _A. lumbricoides._ _A. sp._ _A. texana._ _A. maritima._ _Toxascaris_ _T. limbata._ _Belascaris_ _B. cati._ _B. marginata._ _Lagocheilascaris_ _L. minor._ _Oxyuridæ_ -- _Oxyuris_ _O. vermicularis._ _Mermithidæ_ -- _Mermis_ _M. hominis oris._ (_Agamomermis_) _Ag. restiformis._ Family. *Anguillulidæ.* Genus. *Rhabditis*, Dujardin, 1845. Buccal cavity elongated, with lips. Its chitinous wall uniformly thick. Lateral lines absent. Males with bursa. *Rhabditis pellio*, Schneider, 1866. Syn.: _Pelodera pellio_, Schn., 1866; _Rhabditis genitalis_, Scheiber, 1880; _Rhabditis pellio_, Schn., 1866. Males 0·8 to 1·05 mm. in length; females, 0·9 to 1·3 mm. in length. The posterior extremity of the body of the male has a heart-shaped bursa, and seven to ten ribs on each side; the bursa may, however, be lacking. The spicules measure 0·027 to 0·033 mm. in length, but are never quite alike. The posterior extremity of the female is long and pointed; the vulva lies somewhat behind the middle of the body, the ovary is single, the eggs are oval, 60 µ by 35 µ. This species was found in Stuhlweissenburg by Scheiber in the acid urine (containing albumin, pus and blood) of a woman suffering from pyelonephritis, pneumonia and acute intestinal catarrh; the observer was able to convince himself that the Nematodes which were found during the whole period of the illness lived in the vagina, and were evacuated with the urine. Oerley proved that this species had long been known; during its larval stage (_Anguillula mucronata_, Grube, 1849) it lives in earthworms; in its adult stage it lives in decomposing matter in the soil. By introducing individuals of this species into the vagina of mice, Oerley succeeded in obtaining infection and multiplication (facultative parasitism). These Nematodes must in some such way have got into the vagina of Scheiber’s patient. Two other cases described by Baginsky and Peiper probably belonged to the same or a nearly related species. *Rhabditis niellyi*, Blanchard, 1885. Syn.: _Leptodera niellyi_, Blanchard, 1885. In 1882 Nielly had a cabin-boy, aged 14, under observation in Brest. The lad had never left the neighbourhood of Brest, and had suffered from itching papules on the skin for five or six weeks; in the papules the observer found one or several rhabdites, measuring 0·33 mm. in length by 0·30 mm. in breadth. Their cuticle presented a delicate transverse striation; the intestine was the only internal organ recognizable, and it opened somewhat in front of the posterior extremity. Therefore, it must have belonged to the rhabditis-like larva of a Nematode, the adult stage of which is unknown. The manner of infection was established almost certainly by a further observation of Nielly’s: at the commencement of the illness small Nematodes were found in the blood of the patient; later on, however, they disappeared, neither were Nematodes found in the fæces, urine or sputum. Therefore it must be concluded that the cabin-boy, who was in the habit of drinking water from brooks, had thus ingested embryo-containing eggs of a Nematode; the young hatched out in the intestine, perforated it, reached the blood and then settled in the skin; but, on the other hand, the entry may have been direct through the skin. In connection with the foregoing, reference should be made to a communication by Whittles, insufficient from a zoological point of view. In a case of hypertrophic gingivitis occurring in a female patient, aged 19, who had never left Birmingham, he found Nematode larvæ in the periosteum of the upper jaw, which was excised after extraction of the right premolar; the genital rudiment could be recognized in them. Similar larvæ were found in the same patient in abscesses in various regions of the skin, and in the case of her mother in the blood. The author considers that the infection took place through a dog, and refers to the case of O’Neil (1875), who found Filariæ in the skin (in the condition known as “craw-craw”), referred by Manson to _Filaria perstans_. O’Neil’s case was quoted, and attributed to _Filaria sanguinis hominis_. In conclusion, the author states that he has repeatedly found Nematode larvæ in the blood of persons who suffered from pruritus; in his opinion the parasite had been imported through the agency of troops returned from South Africa. Glatzel found true Filaria larvæ in a pustule of a cutaneous eruption of the trunk and extremities in a patient at Dar-es-Salam. Skin diseases which are caused by young Nematodes are also observed in dogs (Siedamgrotzky, Möller, J. G. Schneider, Künnemann), foxes (Leuckart), and horses (Semmer). Zürn found young Nematodes (_Anguillulidæ_) also in pig’s flesh. In Künnemann’s case it was shown that the adult Rhabdites lived in the straw upon which the dog lay. *Rhabditis*, sp. In the fluid obtained by lavage from the stomach of a female patient, aged 16, suffering from ozæna, O. Frese found during two consecutive months Rhabdites of various ages, 0·275 to 0·64 mm. in length, the adults all with eggs; males were not found; transmission into rabbit’s stomach failed, but they could be kept alive in much diluted hydrochloric acid (2 : 1,000) for several weeks. Neither eggs nor larvæ appeared in the fæces of the patient. The nature of the infection, which was perhaps of unique occurrence, remained doubtful. Genus. *Anguillula*, Ehrenberg, 1826. Buccal cavity very small, without lips. Males without bursa, but with a series of papillæ. Lateral lines absent. *Anguillula aceti*, Müller, 1783. Cuticle unstriped, body cylindrical, anterior end tapering but little, posterior end long, pointed. Male up to 1·45 mm. long, 0·024 to 0·028 mm. wide; two pre-anal papillæ, one post-anal; spicules equal, curved, 0·038 mm. long; gubernaculum present; testis extending in front of mid-line of body. Female up to 2·4 mm. long, 0·040 to 0·072 mm. wide; anterior uterus reaching to near the œsophagus, posterior to hind gut. Viviparous; embryos in both or only in one uterine horn, 0·22 mm. long, 0·012 mm. broad. The species is a frequent inhabitant of vinegar (prepared by older methods), and was once observed for some time by Stiles and Frankland in the urine of a woman; the urine had an acid reaction, and once had a distinct odour of vinegar. It was assumed that the patient, who was hysterical and suffered from chronic nephritis, employed vaginal douches with diluted vinegar, perhaps to deceive her physician or to protect herself against conception. According to Ward, Billings and Miller are said to have reported on two other cases. Ill-effects which might be connected with the vinegar eel (_Anguillula aceti_) were not present. Genus. *Anguillulina*, Gervais and Beneden, 1859. Syn.: _Tylenchus_, Bastian, 1864. Characterized by the possession in the buccal cavity of a spine knobbed posteriorly; bursa present; uterus asymmetrical. Numerous species parasitic in plants. *Anguillulina putrefaciens*, Kühn, 1879. Syn.: _Tylenchus putrefaciens_, Kühn; _Trichina contorta_, Botkin, 1883. In 1883 Botkin (_Pet. klin. Wochenschr_., 1883) found a small Nematode, which was, however, entirely mistaken, in the material vomited by a Russian; this was not a species of Trichinella, but an _Anguillulina_ living in onions which had already, in 1879, been described by Kühn as _Tylenchus putrefaciens_; the Nematodes got into the stomach with the onions, causing nausea and vomiting. Family. *Angiostomidæ*, Braun, 1895. Genus. *Strongyloides*, Grassi, 1879. Syn.: _Pseudorhabditis_, Perroncito, 1881; _Rhabdonema_, Leuckart, 1882, _p.p._ The genus is insufficiently defined. The parasitic form possesses a simple mouth opening directly into the long cylindrical œsophagus which occupies the anterior third of the body. The free-living forms possess a small buccal cavity; the œsophagus is short, with a double bulb, in the hinder one there is a *Y*-shaped chitinous valve; two spicules of equal size. *Strongyloides stercoralis*, Bavay, 1877. Syn.: _Anguillula intestinalis_ et _stercoralis_, Bavay, 1877; _Leptodera intestinalis_ et _stercoralis_, Cobb.; _Pseudorhabditis stercoralis_, Perroncito, 1881; _Rhabdonema strongyloides_, Leuckart, 1883; _Strongyloides intestinalis_, Grassi, 1883; _Rhabdonema intestinale_, Blanchard, 1886. [Illustration: FIG. 270.--_Strongyloides stercoralis_, female: parasitic generation from gut of man. × 70. (After Looss.)] [Illustration: FIG. 271.--_Strongyloides stercoralis_, male: free-living generation. × 170. (After Looss.)] In 1876, a number of French soldiers returned to Toulon from Cochin China suffering from severe diarrhœa. Dr. Normand, under whose treatment they were, discovered a large number of Nematodes in the evacuated fæces, and Bavay described them as _Anguillula stercoralis_. Soon after Normand, at the _post-mortem_ of five patients who had died of Cochin China diarrhœa, found numerous other Nematodes in the intestine, from the stomach to the rectum, in the bile-ducts and in the pancreas, and these he handed over to Bavay. The latter diagnosed another species, and described them as _A. intestinalis_. Both forms were then regarded as the cause of Cochin China diarrhœa until, in 1882, Leuckart was able to demonstrate that the two forms are only two succeeding generations of the same species, of which the one (_A. intestinalis_) lives parasitically in the intestine, whereas its young (_A. stercoralis_) attain the open, where they come to maturity and propagate. The young of these again live parasitically. There thus exists the same heterogony as was discovered by Leuckart in _Angiostomum nigrovenosum_ of frogs, which heterogony, indeed, according to v. Linstow, appertains to the entire family of the _Angiostomidæ_. (1) The parasitic generation (strongyloid or filariform ♀) is quite colourless and cannot be seen _in situ_ even with a lens. To detect them it is necessary to scrape the mucosa of the jejunum and examine the scrapings microscopically. It measures 2·2 mm. in length, and 34 µ to 70 µ in breadth; the cuticle is finely transversely striated; the mouth is surrounded by four lips; the œsophagus is almost cylindrical and a third the length of the entire body. The anus opens shortly in front of the pointed posterior extremity; the vulva is situated at junction of middle and posterior thirds of the body; the uterus has no special ovejector; the eggs measure 50 µ to 58 µ in length, and 30 µ to 34 µ in breadth, and lie in a chain one behind the other (fig. 270). As in the case of _Angiostomum nigrovenosum_, Leuckart considers this stage to be hermaphroditic, the testes degenerating after having functioned; other authors (Rovelli) regard it as a female reproducing by parthenogenesis. (2) The free-living generation (♂ and ♀) has a smooth body, cylindrical, somewhat more slender at the anterior extremity and pointed at the tail end. The mouth has four indistinct lips; the œsophagus is short with a double (rhabditis-like) bulb; there is a *Y*-shaped valve in the posterior bulb; the anus opens in front of the tail end. The males measure 0·7 mm. in length, 0·035 mm. in breadth. Their posterior end is rolled up; the two brown spicules are small (38 µ) and much curved. There is also a gubernaculum. The females measure 1 mm. in length or a little over; 0·05 mm. in breadth. The tail end is straight and pointed; the vulva lies somewhat behind the middle of the body. The yellowish, thin-shelled ova measure 70 µ in length and 45 µ in breadth. As Askanazy has shown, the parasitic form bores deeply into the mucous membrane of the intestine, and frequently into the epithelium of Lieberkühn’s glands, both for nourishment and oviposition. The eggs then develop in the intestinal wall. The eggs which are found in scrapings from the mucosa occur, at least in the case of Strongyloides of the sheep, in chains enclosed in a thin tube or sheath, the origin of which is doubtful; possibly it is the uterus. The eggs themselves are only rarely found in stools, _e.g._, after a strong purge. The larvæ, which are hatched out, and measure 0·2 to 0·25 mm. long by 0·016 mm. broad, again reach the lumen of the intestine,[299] and grow to double or three times that size, until they are passed out with the fæces. They already differ from the parent (♀) in the shape (rhabditiform) of the œsophagus. When the external temperature is sufficiently high (26° to 35° C.), they become sexually mature after moulting. In about thirty hours they are completely developed and copulate, now forming the free-living rhabditiform generation. At lower temperatures the larvæ only moult, but do not escape from the old cuticle and do not develop further. At a temperature of about 25° C. only some of the larvæ attain maturity. [299] As a case published by Teissier shows, they may also abnormally appear in the blood (_Arch. méd. expér. et d’An. path._, 1895, vii, p. 675). [Illustration: FIG. 272.--_Strongyloides stercoralis_, female; free-living generation, × 170. (After Looss.)] [Illustration: FIG. 273.--_Strongyloides stercoralis_: larva from fresh human fæces. × 310. (After Looss.)] The females of the free-living generation (rhabditiform) deposit from thirty to forty eggs, which develop rapidly, sometimes even within the uterus in the case of old females. After the larvæ have emerged from the egg-shell, they measure 0·22 mm. in length, and possess the characteristics of the parents (rhabditiform larvæ). When they have grown to 0·55 mm. they moult, and while losing their own characteristics they acquire the characteristics of their parasitic grandparents (strongyloid or filariform). After about eight days the free-living adult generation in the cultures have disappeared, and all the rhabditiform larvæ have been transformed into strongyloid or filariform larvæ; they then die off unless they reach the intestine. This cycle of development holds good for _Strongyloides stercoralis_ of tropical origin (Bavay, Leuckart, Leichtenstern, Zinn). In the European Strongyloides the free-living generation, as a rule, is absent (Grassi, Sonsino, Leichtenstern, Braun); the rhabditis-like larvæ evacuated with the fæces are transformed into the strongyloid or filariform type of larva (in cultures which are easily made) which will only become adult if introduced into man. [Illustration: FIG. 274.--_Strongyloides stercoralis_: mature filariform larva showing long transparent œsophagus, slender granular intestine and characteristic tip to the tail ending in two small points. × 620. (After Looss).] So that we have these two cycles: (_A_) (1) ♀ parasitic, (2) eggs, the rhabditiform larvæ in fæces, (3) free-living strongyloid or filariform larva, (4) ♀ parasitic. (_B_) (1) (2) (3) as before, then (4) adult ♀ and ♂, free living, (5) eggs, (6) rhabditiform larva, (7) strongyloid or filariform larva, (8) ♀ parasitic. Infection of man results not only from direct entry into the stomach but also, according to van Durme and Looss, through the skin. _Occurrence in Man._--As already mentioned, _Strongyloides stercoralis_ was first observed in persons suffering from so-called Cochin China diarrhœa. From the enormous numbers of parasites evacuated with the fæces, the cause of the disease was apparently evident. It appeared, however, that only some of the soldiers returning from Cochin China and Martinique, and suffering from diarrhœa, harboured Strongyloides (Chauvin). Breton made the same observations in Cochin China and found that only 10·4 per cent. of cases of chronic dysentery, and 8·8 per cent. of chronic diarrhœa, show Strongyloides. Normand, moreover, found that only a few of the Europeans residing in Cochin China are exempt from _S. intestinalis_, yet the people exhibit no intestinal symptoms; if, however, from any cause a catarrhal condition of the intestine supervenes the condition is changed, the parasites appear in larger numbers, and the disorder is considerably intensified. _S. intestinalis_, besides being present in the Indo-China region, also occurs in the Antilles, in Brazil, Africa, and Europe; in 1878 it was discovered in Italy by Grassi and C. and E. Parona; in 1880 it was also found in the labourers working at the St. Gothard tunnel. It was imported into Germany, Belgium, and the Netherlands by Italian labourers. One sporadic case has been observed in East Prussia, and the worm has also been reported from Siberia. In mammals the following species are found: _Probstmayria_ (_Strongyloides_) _vivipara_, Ransom, 1907, in _Equus caballus_; _Strongyloides fülleborni_, v. Linst., in _Anthropopithecus troglodytes_ and _Cynocephalus babuin_. Their development is, so far as is known, the same as that of _Strongyloides stercoralis_ (v. Linstow, _Centralbl. f. Bakt., Path. u. Infektionsk._, 1905, Orig. xxxviii, p. 532). Family. *Gnathostomidæ.* Genus. *Gnathostoma*, Owen, 1836. Syn.: _Cheiracanthus_, Diesing, 1839. Easily recognizable by the numerous spines which cover the entire body or only the anterior extremity, and terminate in several points; head globular and beset with bristles; mouth with two lips; two spicules; vulva situated behind the middle of the body. *Gnathostoma siamense*, Levinsen, 1889. Syn.: _Cheiracanthus siamense_, Lev., 1889. Female measures 9 mm. in length, 1 mm. in breadth. There are eight rows of simple spines on the head; the armature of spines extends over the anterior third of the body only; each spine on the anterior region of the body spreads into three points, of which the middle one is the longest; the posterior spines are simple; they gradually become smaller and then disappear entirely. The vulva is situated behind the middle of the body. _Male._--10·5 mm. long by 0·6 mm. broad. Head terminates in a globular swelling with two large lips. Neck 3 mm. broad. In front of neck eight rows of simple spines directed backwards. Anterior half of body with cuticular laminæ, posterior unarmed. Two pre-anal and two post-anal papillæ. Bursa wanting. Spicules 1·1 and 0·4 mm. respectively. Leiper considers _Gnathostoma siamense_ to be identical with _Gnathostoma spinigerum_. The single specimen described by Levinsen was found by Deuntzer in Bangkok (Siam), and was obtained from a young Siamese woman who suffered from a small tumour of the breast which had developed in the course of a few days. After the disappearance of the tumour, nodules the size of beans were found in the skin; out of one of these the worm was obtained. The same observer saw this affection in two other persons. A closely related species, _Gnathostoma spinigerum_, Ow., lives in the stomach of wild cat (_Felis catus_), puma (_Felis concolor_), tiger (_Felis tigris_), and domestic cat (India); another species, _Gnathostoma hispidum_, Fedsch., 1839, in the stomach of pigs in Turkestan, Annam, Hungary, Congo, and by Collin in the stomach of an ox (Berlin). _Gnathostoma_ sp. in pariah dogs, Calcutta. _Gnathostoma_ sp. in monkeys, French Guiana. They produce large fibrous thickenings in the stomach wall. [Illustration: FIG. 275.--_Gnathostoma siamense_: to the left, the entire worm (8/1); to the right the head seen from above, with two fleshy lips (about 40/1). (After Levinsen.)] *Gnathostoma spinigerum*, Owen, 1836. Cuticle of bulb with eight rows of chitinous laminæ with their posterior edges notched into spines. The laminæ on the anterior portion of the body are similar trident laminæ. In the middle of the body, the laminæ are simple and conical, cuticle posteriorly is unarmed. Mouth with two fleshy lips. Male 5 mm. long by 0·5 mm. broad; tail spiral, four pairs of papillæ. Female about twice as long; tail straight, trilobed. Family. *Dracunculidæ*, Leiper, 1912. Genus. *Dracunculus*, Kniphoff, 1759. Anterior end rounded with a cuticular thickening or shield. Mouth triangular with two lips. Alimentary canal atrophied. *Dracunculus medinensis*, Velsch, 1674. Syn.: _Vena medinensis_, Velsch, 1674; _Dracunculus persarum_, Kämpfer, 1694; _Gordius medinensis_, Linné, 1758; _Filaria dracunculus_, Bremser, 1819; _Filaria æthiopica_, Valenciennes, 1856; _Dracunculus medinensis_, Cobbold, 1864; _Guinea worm_, _Medina worm_. The females attain a length of 50 to 80 cm., or even more, and average 1·5 to 1·7 mm. in diameter. They are whitish or yellowish in colour. The anterior extremity is roundish and bears a cuticular thickening or shield. The triangular mouth opening is surrounded by two projections or lips, behind which on the shield there are two lateral and four sub-median papillæ; the posterior end terminates in a spine, ventrally directed, and about 1 mm. in length; the alimentary canal below the œsophagus is atrophied, but not entirely obliterated; anus absent; the lateral lines are very flat. The greater part of the body is occupied by the long uterus, in which a great number of young larvæ are always found. The ovaries probably lie at the ends of the uterus; the vulva lies just behind the cephalic shield. During parturition the uterus is prolapsed through this opening. The male is almost unknown. Leiper in an experimentally infected monkey found two males 22 mm. long, one from the psoas muscle, the other from the connective tissue behind the œsophagus. _Occurrence._--_Filaria medinensis_ has been known since the most remote period. The “fiery serpents” that molested the Israelites by the Red Sea, and which Moses mentioned, were probably filariæ. The term Δρακὁντιον occurs in Agatharchides (140 B.C.). Galen called the disorder dracontiasis; the Arabian authors were well acquainted with the worm. It is found not only in Medina or Arabia, but also in Persia, Turkestan, Hindustan. The Guinea worm is also widely distributed in Africa, on the coasts as well as in the interior. It occurs in the Fiji Islands. It was carried to South America by negro slaves, but is said at the present time to exist in only quite a few places (British Guiana, Brazil [Bahia]); it is also observed in mammals (ox, horse, dog, leopard, jackal [_Canis lapuster_], etc.). _Dracunculus medinensis_ in its adult stage lives in superficial ulcers on the body surface; it is seen most frequently on the lower extremities, more especially in the region of the ankle, but it also occurs in other parts of the body--on the trunk, scrotum, perineum, on the upper extremities, and in the eyelids and tongue. Sometimes there is only one ulcer and one worm, but more commonly several. It attacks man without distinction of race, age or sex. It is observed most frequently during the months of June to August. [Illustration: FIG. 276.--Guinea worm (_Dracunculus medinensis_). (After Leuckart.)] [Illustration: FIG. 277.--Anterior extremity of Guinea worm, showing dorsal and ventral lips, one lateral and two submedian papillæ and the lateral line. (After Leuckart.)] [Illustration: FIG. 278.--_Dracunculus medinensis_. _a_, anterior extremity seen end on; O, mouth; P, papillæ; _b_, female reduced more than half; _c_, larvæ enlarged. (After Claus.)] _Life history._[300]--When about a year old the worm seeks the surface of the body and produces there a thickening as big as a florin. Over this a vesicle forms which eventually ruptures, and at the bottom of the ulcer can be seen a hole from which a part of the worm may project. On bathing the sides of the ulcer with water, a drop of fluid, at first clear then milky, exudes. This contains numerous larvæ. In other cases a thin tube an inch long is prolapsed (through the vulva). This is probably the uterus, but the mechanism of parturition is not clearly known. It lasts for about a fortnight. An abundant supply of larvæ can be got by placing wet compresses on a _fresh_ ulcer. In a few hours a mass of larvæ is obtained. [300] The larvæ resemble those of _Cucullanus elegans_ parasitic in the perch (_Perca fluviatilis_). The larvæ of this species develop in Cyclops sp. Fedschenko in 1870, at Leuckart’s suggestion, succeeded in observing the invasion of Cyclops by Guinea worm larvae. They penetrate not _per os_ but through the exoskeleton. Newly hatched larvæ (in bananas) will cause infection of monkeys. The larvæ are 500 µ to 750 µ by 15 µ to 25 µ, with a long slender tail about one-third of the total length. The cuticle is transversely striated. The body is flattened. They possess an œsophagus and gut. At the anus there are apparently glandular structures. [Illustration: FIG. 279.--Transverse section of female Guinea worm; _u._, uterus containing embryos; _i._, intestinal canal; _o._, ovary. (After Leuckart.)] The larvæ live and move actively in water for about two days, the majority dying on the third (Leiper). If a number of Cyclops sp. have been collected and isolated in clean water, and the larvæ are now added, the further development can be traced. The larvæ enter the Cyclops, according to most authorities, by penetrating the exoskeleton, but according to Leiper this is impossible; they must enter by the mouth and penetrate the gut in order to reach the body cavity. In eight days moult 1 takes place, the striated cuticle being cast off. In ten days moult 2 takes place. In five weeks the larva is mature. If now the infected Cyclops is placed in 0·2 per cent. HCl solution the Cyclops is killed immediately, but the larvæ are stirred into activity, escape from the body, and swim about in the acid. This suggests that infection in nature probably takes place by the swallowing of infected Cyclops; Leiper, by feeding Cyclops containing mature larvæ to a monkey, found in it, _post mortem_ six months later, two immature females 30 cm. long and two males 22 mm. long. In certain areas the new cases occur principally in June. Five weeks later the larvæ will become mature in Cyclops, so that infection of Cyclops is taking place in July or August, and from then to June about ten months elapse, giving the period of development in man. _Pathology._--The initial induration is accompanied by itching. Urticarial eruptions are described in Dahomey and Mauretania accompanied by fever, rigors, blood-shot conjunctiva, and prostration resembling fungus poisoning. Symptoms last for one to two days, later the worms appear on the surface. [Illustration: FIG. 280.--_Cyclops virescens_, ♀. 8, Female, ventral view, × 120; 9, anterior antennæ × 240; 10, urosome and last thoracic segment, × 240; 11, foot of first pair, × 320; 12, 15, 16, foot of second, third and fourth pairs, × 240; 14, foot of fifth pair, × 440; 13, last thoracic segment and first segment of urosome of male, × 240.] If the worm is ruptured in an attempt to extract it, disastrous results may occur through the escape of the larvæ into the tissues: fever, inflammation, abscess, sloughing, ankylosis, even death from sepsis. Eosinophilia is often marked, 11 to 13 or even 50 per cent. _Extraction._--(1) The native method consists in rolling the worm round a stick; 1 in. to 2 in. are extracted each day, the process taking about a fortnight; (2) Emily used injections of 1 in 1,000 sublimate into the swelling or into the worm itself fixed by a ligature. (3) Béclère chloroforms the worm; (4) the worm can be more easily removed when all the embryos have been deposited (two to three weeks). _Cyclopidæ._--Cephalothorax ovate, clearly separated from abdomen. Anterior antennæ of female when bent back scarcely ever stretch beyond the cephalothorax. The second antennæ are unbranched. First four pairs of feet two-branched, outer branches three-jointed. The fifth pair of limbs are rudimentary alike in both sexes, usually one-jointed. There is no heart. The female has two egg sacs containing about fifty eggs. Genus. *Cyclops*, Müller, 1776. Mandible palp rudimentary, reduced to a tubercle bearing two branchial filaments. Maxillary palp rudimentary (obsolete). Lower foot-jaw non-prehensile. Head ankylosed to first thoracic segment. Family. *Filariidæ.* Sub-family. *Filariinæ.* The residue after exclusion of the _Arduenninæ_ and _Onchocercinæ_. Genus. *Filaria*, O. Fr. Müller, 1787. Very long, slender Nematodes, without excretory vessels or excretory pore, the males of which are usually considerably smaller than the females. Mouth round, without lips, unarmed. The lateral lines occupy one-sixth of the circumference of body. The tails of the males are bent or spirally rolled, and bear little wing-like appendages. The two spicules are unequal; almost always there are four pre-anal papillæ, but the number of post-anal papillæ varies. The vulva is always situated at the anterior extremity. Parasitic chiefly in the serous cavities and in the subcutaneous connective tissue. Insufficiently defined. *Filaria bancrofti*, Cobbold, 1877. Syn.: _Trichina cystica_, Salisbury,[301] 1868 (_nec Filaria cystica_, Rud., 1819); _Filaria sanguinis hominis_, Lewis, 1872; _Filaria sanguinis hominis ægyptiaca_, Sonsino, 1875; _Filaria wüchereri_, da Silva Lima; _Filaria sanguinis hominum_, Hall, 1885; _Filaria sanguinis hominis nocturna_, Manson, 1891; _Filaria nocturna_, Manson, 1891. [301] C. W. Stiles (“American Medicine,” 1905, ix, p. 682) is of the opinion that Salisbury’s _Trichina cystica_ is identical with _Oxyuris vermicularis_. These parasites of man were for a long time only known in their larval stage. They were discovered in 1863 in Paris by Demarquay, in the hydrocele fluid of a Havanese emptied by puncture; they were next observed by Wücherer, in Bahia, in the urine of twenty-eight cases of tropical chyluria; they were likewise observed in North America by Salisbury, who gave them the name of _Trichina cystica_. The next discoveries (in Calcutta, Guadeloupe, and Port Natal) related to chyluria patients, until Lewis discovered the larvæ in the blood of man (India), and found they were almost always present in persons suffering from chyluria, elephantiasis, and lymphatic enlargements; he also, in exceptional cases, found them in apparently healthy persons (_Filaria sanguinis hominis_). Lewis and Manson studied the disease and the filariæ of the blood very minutely, and became aware that the filariæ were sucked up by mosquitoes with the blood. Manson described the metamorphoses that take place within the body of the mosquito. The adult female was discovered in Queensland by Bancroft, and soon after Lewis found it in Calcutta; it was described by Cobbold as _F. bancrofti_. The male was first seen by Bourne in 1888. [Illustration: FIG. 281.--_Filaria bancrofti._ 1, Anterior portion of male; 2, two rows of papillæ on head; 3, papillæ of tail of male; 4, cloaca of male showing tips of spicules and gubernaculum; 5, the spicules and gubernaculum of male. (After Leiper.)] Head bougie-like, _i.e._, separated by a narrowing from the neck, having two rows of minute papillæ. Cuticle has extremely fine striations. _Female._--50 to 65 mm. long by 1·5 to 2 mm. broad. Vulva 0·4 to 0·7 mm. behind the head. Anus about 1/4 mm. from the tip of the tail (vulva 1 to 1·3 mm. from head, and anus 0·17 to 28 mm. from tail according to other authors). The vagina is a muscular tube forming three bold loops, and has terminally a pyriform enlargement. Uterus double (or single). Ovoviviparous. _Male._--25 to 30 mm. long by 0·1 mm. thick (40 by 0·1 mm. according to various authors). Probably two pairs of pre-anal papillæ, eight pairs of peri-anal, two pairs of post-anal papillæ, and one pair terminal. Tail curved. Two spicules, 0·2 and 0·6 mm. respectively, and a cup-like gubernaculum. The long spicule is cylindrical, expanded proximally and tapering distally to a filament with wings. At the tip it is spoon-like. The short spicule is of the same diameter throughout. It is gutter-like, coarsely marked. Testis uncoiled, terminating in a snowdrop-like process (Leiper). _Eggs._--40 µ by 25 µ. They do not appear to possess a true shell, but only an embryonal or vitelline membrane secreted by the ovum. _Embryos._--In the posterior part of the uterus eggs occur, in the anterior part embryos; the larvæ at birth measure 127 µ to 200 µ by 8µ to 10 µ. In the blood they measure in the fresh 260 µ by 7·5 µ to 8 µ. In stained films, owing to shrinkage, there is great variation in size, from 154 µ to 311 µ. Probably 260 µ to 285 µ is the average in stained films. _Geographical Distribution._--Europe: Two cases recorded, one from near Barcelona. The patient suffered from hæmato-chyluria and enlarged scrotum with mikrofilariæ in the blood. A second case from Siena. Africa: The filarial index has not been estimated for various parts. In Nigeria it is about 10 per cent. _Habitat._--Lymphatic glands: _e.g._, inguinal, femoral, iliac, lumbar, mesenteric, bronchial, superficial cervical, epitrochlear. Lymphatic vessels: _e.g._, those draining into the receptaculum chyli of the spermatic cord, in the thoracic duct and in various different parts. Organs, etc.: Testis, epididymis, spermatic cord, tunica vaginalis, mammary cyst, and in abscesses. They may occur in masses, but usually only a few (one to eight). Females are commoner than males. Dead and calcified worms are common in the various sites. _Distribution of Larvæ in Body._--These are by no means uniformly distributed, but occur in greater number in the capillaries of the lungs. Besides the lungs they occur in the capillaries of other organs, as the following data of Rodenwaldt show:-- Mikrofilariæ Mikrofilariæ Lungs 134,821† Spleen 1,666 Liver 4,884 Brain 3,833 Kidneys 15,253 Glands 0 {Glomeruli 8,008 Marrow 0 {Parenchyma 7,245 Blood 3,000 † These figures refer to 1 c.c. of each organ, and were estimated by cutting sections of definite thickness (30 µ to 40 µ) and counting the filariæ in a definite area of section, _e.g._, 1/4 cm.^2 The organs before removal from the body have their vessels tied, and are then fixed in hot alcohol. The following data of Rodenwaldt refer to the larvæ of _Filaria immitis_ in the dog. They are commoner in organs than in vessels, and especially in the _capillaries_ of the organs, but in the lungs they appear to be equally distributed in capillaries, arteries and veins. The length of life of larvæ is unknown, but they appear to be destroyed in the kidneys, as dead calcified specimens are fairly numerous in the capillaries of the vasa recta of the medullary substance. Kidneys: mainly in the glomerular capillaries and those of the vasa recta. Liver: in the capillaries of the portal system, especially in those between the interlobular and the central intralobular veins. _Periodicity of Larvæ._[302]--Roughly speaking, the larvæ of _Filaria bancrofti_ are found in the peripheral blood only during the night, disappearing (but not entirely) during the daytime. Their periodicity and that of _Loa loa_ larvæ is shown by the table on p. 394, based on that of Smith and Rivas (_Amer. Journ. Trop. Dis. and Prev. Med._, 1914, vol. iii, p. 361). [302] For determining periodicity measured quantities of blood, _e.g._., 20 mm.^3, should be used. A thick film is made of the whole quantity. The numbers present in this quantity may vary from three or four to 300 or 400. It was discovered by Mackenzie that this periodicity could be reversed by making the patient sleep during the daytime, showing that the phenomenon was in some way dependent on sleep or its attendant phenomena. Rodenwaldt gives the following explanation of the phenomenon of periodicity:-- Mikrofilariæ come to rest in capillaries. After passing up the thoracic duct they would reach the capillaries of the lungs by the superior vena cava. Here they occur in immense numbers. In the case of _Loa loa_ larvæ (which have a diurnal periodicity) some of these are forced out by the increased force and rapidity of the pulmonary circulation during the day, but are able to rest (owing to their sticky sheath?) in the peripheral capillaries on their way to the capillaries of the organs. During the night the force of the current through the lungs is relaxed and consequently they are able to remain in the pulmonary capillaries and do not appear in the capillaries of the systemic circulation. If it is true that the periodicity of _Loa loa_ cannot be reversed by changing the hours of sleep, then the explanation is incomplete. In the case of the larvæ of _Filaria bancrofti_ (which have a nocturnal periodicity), in order to apply the same explanation we must further assume that the mikrofilariæ have less power of resisting the force of the capillary current (_i.e._, are less sticky). They are washed out of the pulmonary capillaries by day and by night, but it is only at night, when the blood stream in systemic capillaries is less rapid, that they are able to rest there. In the daytime they are washed on until they reach the capillaries of the organs (possibly again the lungs). The reversal of the periodicity by sleeping during the daytime admits of a similar explanation. If this explanation be true, then a prolongation of the day conditions, _e.g._, by continued exercise, should result in still keeping the larvæ out of the circulation, but this does not appear to be the case. --------+----------+----------+----------+----------+----------+---------- | Larvæ of | Average | CASE 1. | Average | CASE 2. | Average | _L.loa_ | 132. | _F. | 1,000 | _F. | 1,570 | in equal |Deviations|bancrofti_| (about). |bancrofti_| (about). |quantities| from | larvæ |Deviations| larvæ |Deviations | of blood | average |in 1 c.c. | from |in 1 c.c. | from | | | of blood | average | of blood | average --------+----------+----------+----------+----------+----------+---------- 2 a.m. | 9 | - 123 | 3,500 | + 2,500 | 6,500 | + 3,930 4 a.m. | 11 | - 121 | 3,200 | + 2,200 | 5,200 | + 3,630 6 a.m. | 41 | - 91 | 2,800 | + 1,800 | 2,000 | + 430 8 a.m. | 168 | + 36 | 900 | - 100 | 1,100 | - 470 10 a.m. | 298 | + 166 | 210 | - 790 | 350 | - 1,220 12 noon | 531 | + 389 | 30 | - 970 | 50 | - 1,520 2 p.m. | 252 | + 120 | 20 | - 980 | 40 | - 1,530 4 p.m. | 146 | + 14 | 10 | - 990 | 30 | - 1,540 6 p.m. | 91 | - 41 | 40 | - 960 | 40 | - 1,530 8 p.m. | 23 | - 99 | 60 | - 940 | 100 | - 1,470 10 p.m. | 5 | - 127 | 600 | - 400 | 800 | - 770 12 mid- | 5 | - 127 | 750 | - 250 | 2,600 | + 1,030 night| | | | | | --------+----------+----------+----------+----------+----------+---------- Total | 1,580 | -- | 12,120 | -- | 18,810 | -- --------+----------+----------+----------+----------+----------+---------- In certain countries, _e.g._, Fiji, Samoa, Philippines, West Africa, larvæ, apparently those of _Filaria bancrofti_, show no periodicity. In Fiji the usual intermediate host is _Stegomyia pseudoscutellaris_, a day-biting mosquito, so that possibly, as Bahr suggests, the mikrofilariæ have partly adapted themselves to the habits of their intermediate host, as the nocturnal mikrofilariæ are adapted for transmission by a nocturnal feeding mosquito, _e.g._, _Culex fatigans_, but how this could come about is a mystery. It is not certain in all cases whether the non-periodic mikrofilariæ really belong to _Filaria bancrofti_; some may be _L. loa_ larvæ, or possibly unknown larvæ. An exact morphological description of these larvæ is therefore always necessary. _Preservation of Living Larvæ._--Blood from the vein (or finger puncture) is shaken up with twenty times its volume of sterile 0·9 per cent. salt solution, and kept in an ice cupboard (Fülleborn). _Concentration of Larvæ._--(_a_) The above mixture is hæmolysed with water and then sufficient salt solution added to make up to 0·9 per cent. The solution is allowed to stand or can be centrifugalized. (_b_) The blood is mixed with sodium citrate and centrifugalized; the larvæ are found in the leucocytic layer (Bahr). (_c_) Allow blood to clot in a small tube; the larvæ appear on the surface of the clot and are so got in pure serum. A drop of blood may also be allowed to clot on the slide; the larvæ are found in the clear areas of serum. (_d_) Hæmolyse blood with water or acetic acid. Centrifugalize, make smears from, or examine the sediment. _Removal of Red Corpuscles._--The blood film is allowed to stand for some minutes in a moist atmosphere. The staining solution is sucked through with blotting paper: the larvæ stick to the slide, while the corpuscles are washed out. _Morphology of Larvæ._--Wet staining: Azur II one part, 0·9 per cent., salt solution 3,000, or very dilute Giemsa or ripened methylene blue or neutral red solutions. Place a drop on the slide and add a drop of blood to this. The larvæ remain alive for one or more days; it sometimes takes twenty-four hours to stain some particular structure. Differentiation by drawing through weak eosin solution is often useful. This method is the best for finest details. The excretory pore, anal pore, excretory cell, and chief “genital” cell stain first, then the matrix cells and finally the column of nuclei. Wet fixation and staining: The blood is spread on a large cover-glass--floated on the surface of 70 per cent. alcohol heated to about 70° C. Wash in water, (1) overstain with 1 in 1,000 azur II solution, warming slightly; (2) differentiate with (_a_) absolute alcohol (containing, if necessary, a trace of HCl), or (_b_) with absolute alcohol 96 per cent. ninety parts, anilin oil ten parts; (3) clear in origanum, bergamot or cajeput oil; (4) mount in balsam. Or stain with hæmatoxylin, _e.g._, Mayer’s glycerine alumhæmatein, heating till slightly steaming. Differentiate with acid (2 per cent. HCl) alcohol if overstained. Clear and mount as above. Dry fixation and staining: (1) With azur II as above, or (2) with hæmatein (warm). Examine the dried films in the usual way without a cover-glass. The azur stains the excretory and genital cells clearly. Thick films: (1) The blood is smeared out fairly thickly over an area as big as a sixpence. (2) Dry _quickly_ to prevent shrinking, using carefully a spirit lamp in a moist climate. (3) Place films downwards in water for a few minutes. (4) Fix in alcohol. (5) Stain with azur II, 1 in 1,000. Differentiate as above. Examine as a dry film. This method suffices for showing the excretory cell and the G1 cell; or (6) Stain with hæmatein (slightly steaming), especially for the column of nuclei and the sheath. The fixation in alcohol in this case may be omitted. (7) The removal of the hæmoglobin and the fixation may be combined by using Ruge’s mixture (formalin 2 per cent., containing 1 per cent. acetic acid) or acetic alcohol (glacial acetic 1, alcohol 3).[303] [303] [Acetic alcohol does well for detecting crescents in thick films of malaria blood.--J. W. W. S.] _Structure of Larvæ._--(1) Subcuticular cells: By vital staining, at intervals underneath the cuticle are seen a series of spindle-shaped cells--the _subcuticular matrix cells_ of Rodenwaldt, the _muscle cells_ of Fülleborn. There are thirty or forty or more of these. (2) Nerve ring: Appears as a break in the nuclear column about 20 per cent. of total length from the head. (3) Excretory system: Consists of a lateral spherical hollow excretory pore which shows a radial striation. Connected with the pore is an excretory cell which appears to be canalized. _Excretory pore_, 29·6 per cent. of length from head. _Excretory cell_, 30·6 per cent. of length from head. (4) “Genital” cells and anal pore: Consists of a pore opening ventrally on a very fine papilla with which are connected four other cells in series, the chief “genital” cell (G1) being some distance from the three others, which lie close to the pore. G1, 70·6 per cent., anal pore, 82·4 per cent. of length from head. (5) Internal body, viscus, or reserve material: Best shown by vital staining with neutral red. This is a granular strand-like body extending from 52·7 per cent. to 65 per cent. of length from head. (6) Tail end: (i) Rod-like structures resembling those in the head, 90 per cent. of length. (ii) The column of nuclei extends to 95 per cent. of length, so that the terminal portion is free from nuclei. (7) Mouth: Terminal according to some authors, lateral according to others. Some describe a fang on the head, others not. By vital staining and eosin differentiation two rod-like structures with mushroom-like caps can be seen behind the head. (8) Cuticle: Transversely striated. There is a longitudinal break in the striation on each side corresponding to the lateral lines. The striation is best shown by vital staining with azur II and eosin differentiation. (9) Column of nuclei: These nuclei of the gut cells form the main feature in ordinary dry films stained with hæmatoxylin. They are separated by a space from the subcuticular cells. [Illustration: FIG. 282.--_Mf. bancrofti_ in thick film, dried and stained with hæmatoxylin: 1, shrunken; 2, unshrunken. × 1,000. (After Fülleborn)] DISTINCTION BETWEEN _Mikrofilaria bancrofti_ AND _Mikroloa loa_. _Dry Films, Hæmatoxylin Staining_:-- _Mf. bancrofti._ _Ml. loa._ (1) In graceful curves (but only (1) Kinked. if quickly dried). (2) Tip of tail free from nuclei. (2) Nuclei extend to tip. (3) Column of nuclei separated by (3) Not so distinctly. a space from the cuticle. _Azur Staining_:-- (4) G1 cell small, easily overlooked. (4) G1 cell large, stains deep blue, cell protoplasm = twice width of larva, easily seen. (5) Excretory cell close to excretory (5) Excretory cell farther pore, 2 per cent. of length. from pore, 4 per cent. of length. _Vital Staining with Neutral Red_:-- (6) Internal body or reserve material (6) Not shown. clearly shown. _Life History._--In the stomach of the mosquito the larvæ cast their sheath in the thickened blood in one to two hours. In twenty-four hours the majority have reached the thoracic muscles, where development proceeds. They are at first immobile and of a “sausage” form (110µ by 13 µ), with a short spiky tail. In three to five days the œsophagus is formed, the larva now being 0·5 mm. long. The larva appears to moult at this time. After the gut is formed papillæ, three or four in number, appear at the tail end. In two to three weeks the larvæ are 1·5 mm. long. They now leave the thorax and reach the labium, but they may be found in various parts of the body, _e.g._, the legs. They bore through Dutton’s membrane and so arrive on the surface of the skin, which they rapidly enter. Their development in man is unknown, but it may be very long, as children are not infected till 4 to 5, or even 10 years old, but this may be due to unknown causes. Development takes place in numerous mosquitoes. Anophelines: _Myzomyia rossii_, _Pyretophorus costalis_, _Myzorhynchus sinensis_, _Myzorhynchus barbirostris_, _Myzorhynchus peditæniatus_. Culicines: _Culex pipiens_, _Culex fatigans_, _Culex skusei_, _Culex gelidus_, _Culex sitiens_, _Culex albopictus_, _Stegomyia fasciata_, _Stegomyia pseudoscutellaris_, _Stegomyia gracilis_, _Stegomyia perplexa_, _Mansonioides uniformis_, _Mansonioides annulipes_, _Scutomyia albolineata_, _Tæniorhynchus domesticus_. Partial development takes place in other species. [Illustration: FIG. 283.--Schematic drawings of the anatomy of _Ml. loa_ and _Mf. bancrofti_ combined from specimens stained in different ways. The position of the organs has not been based on the average values of a large series of specimens, but on that of a single specimen. G1, chief genital cell; G2–4, other genital cells; Ex.-C., excretory cell; Ex.-P., excretory pore; A-P., anal pore; N., nerve ring. Magnification circa 1,000. (After Fülleborn).] _Pathology._--Among the conditions which _Filaria bancrofti_ is believed to produce are lymphangitis, varicose glands, especially inguinal and epitrochlear, chyluria, chylocele, lymph scrotum, orchitis, abscess, and elephantiasis. The evidence that these so-called “filarial diseases” are produced by _F. bancrofti_ is (1) geographical and statistical; (2) pathological. Bahr has contributed evidence of the former kind from his researches in Fiji, on which we may base the following statements:-- (1) The prevalence of filarial diseases is proportional to the prevalence of _Mikrofilaria bancrofti_ in the blood. Thus in four villages examined by him he got the following figures:-- Village A Village B Village C Village D per cent. per cent. per cent. per cent. _Mf. bancrofti_ 12·5 25 31 33 Filarial diseases 29 39 58 34 Total population 168 114 425 222 (2) Out of 257 people with _Mf. bancrofti_ in the blood, 153 were suffering from filarial diseases, _i.e._, 59 per cent. (3) Whereas of 672 people without _Mf. bancrofti_ in the blood, only 263 were suffering from filarial diseases, _i.e._, 37·6 per cent. (4) Again out of 416 people suffering from filarial disease, 153 showed _Mf. bancrofti_ in their blood, _i.e._, 36·7 per cent. It is generally assumed that all people suffering from filarial disease show at some (presumably early) stage larvæ in the blood; but we do not consider that this must necessarily be so. It appears to us quite possible that living adult filariæ may be present in the body, producing disease, without their larvæ appearing in the blood. The absence of larvæ from the blood in 63·3 per cent. of persons suffering from filarial disease is, however, generally explained otherwise. The adults which occur in enlarged glands, etc., get eventually destroyed by inflammatory reaction, so that larvæ are no longer being produced, while the enlarged gland, etc., which the adults have produced remains. This explanation assumes that the larvæ of the original worm die in the circulation or elsewhere, _e.g._, kidney, but we have no evidence as to the duration of life of larvæ in the human body; but also it assumes that a person cannot be reinfected with filaria, for otherwise there is no reason why the diseased should not be infected in the same proportion as the non-diseased. But assuming the explanation to be true, it would explain why a diseased population show larvæ in only about one-third of the cases. It must be borne in mind also that the figures are rather small. _Pathology._--In order to explain the effects which do or may be expected to occur from obstruction of lymphatics, it is necessary to have an accurate knowledge of the distribution and connections of lymphatic vessels (and glands) and the anastomoses of these vessels. We can only briefly summarize our knowledge here. We should recall also that considerable destruction or obstruction of lymphatics or glands may occur without necessarily producing any lymphatic obstruction, at least, of a permanent nature, _e.g._, when a mass of lymphatic glands is destroyed by a bubo in the groin or, again, when a carcinomatous mass of glands is removed from the axilla. Again, to take the case of chyluria--where it is generally assumed that obstruction must occur higher up than the point at which the intestinal lacteals enter the juxta-aortic glands--this disease may occur, _e.g._, in temperate regions, quite apart from such obstruction. It is true that some of these cases of chyluria are not cases of chyle in the urine, but, as little or no fat is present, lymphuria. These do not require the above assumption, but seeing that true chyluria may apparently occur without such obstruction, we should be cautious about explaining this and other symptoms on the basis of obstructions which theory may demand, for only too often there are no _post-mortem_ facts at our disposal. Lymphangitis: What this is due to is unknown. There is no actual evidence of the occurrence of adults in the inflamed vessel. Complete disappearance, not to reappear, of (non-periodic) mikrofilariæ from the blood has been shown by Bahr and others to occur within twenty-four hours after an attack of lymphangitis, orchitis adenitis or simply a high temperature. This mysterious phenomenon requires explanation. If the mikrofilariæ were being killed by the attack, their dead bodies should still be found in the blood; or if the adults were being killed, for all we know to the contrary, the larvæ might well survive. We consider there is no evidence that either are affected, but that for some reason, as little understood as in periodicity, the larvæ now remain in the organs. Abscess: In Fiji, by Bahr, they have been found in the substance of various muscles, _e.g._, quadriceps extensor, latissimus dorsi, serratus magnus, in the popliteal space, groin, axilla, and over the internal condyle of the humerus, and in the upper extremity they are frequently infected with cocci. They not infrequently contain fragments of dead adult filariæ. Their mode of origin is not clear. They form nearly 30 per cent. of cases of filariasis in Fiji. Of 95 cases, 41 showed mikrofilariæ in blood, 54 did not. Hydrocele and enlarged testis: In Fiji they form about 10 per cent. (36 out of 343) of cases of filariasis. The fluid is usually sterile; mikrofilariæ were present in the fluid in 1 out of 11 cases. In the wall numerous calcified adult filariæ may be found. The walls consist chiefly of hypertrophied muscle with fibrous tissue, dilated blood-vessels and lymphatics, the lining epithelium of which appears to be absent; of 38 cases 14 had mikrofilariæ in the blood, 24 had not. Most of the cases are associated with elephantiasis of the scrotum (11 out of 12 cases). Enlarged glands form over 40 per cent. (153 out of 343) of cases of filariasis, so that they are the commonest expression of filariasis met with in Fiji. The glands are enlarged, fibrotic, and the trabeculæ are thickened. The lymphatics are thickened or represented merely by fibrous tissue. The gland also shows dilated blood-vessels and numerous spaces filled with lymph. Giant-cells are common in those glands which contain remnants of filariæ. Masses of lymphocytes enclosed by inflammatory or fibrous tissue are common. Eosinophile cells are also extremely common, not only in the fibrous tissue of the glands, but in other inflammatory or fibrotic conditions: in other organs living or calcified filariæ are “usually” present. Only about 33 per cent. show mikrofilariæ in the blood. The epitrochlear gland is frequently enlarged in Fiji. Breinl has examined enlarged glands and finds loose vascular fibrous tissue with lymphocytic invasion. In parts, the lymphocytes collect into areas 200 µ to 800 µ in diameter. The lymph tissue surrounding the spermatic cord showed abundance of vessels--(1) large, (2) small. The large had thick walls and wide lumina. In other cases the lumina were nearly filled by a thrombus of newly formed, fine, loose connective tissue. Varicose glands: In about 7 per cent. (24 out of 343 cases) of filariasis, mikrofilariæ are found in the blood in 50 per cent. (12 out of 24). _Elephantiasis._--Elephantiasis scroti is associated with hydrocele in 50 per cent. of cases (12 out of 23); in 65 per cent. of cases (15 out of 23) there are associated enlarged glands in one or both groins, though also hydrocele and enlarged glands occur without elephantiasis scroti. In 13 out of 27, _i.e._, about 50 per cent., cases of elephantiasis in various regions, no associated enlargement of glands is found. Elephantiasis forms in Fiji less than 10 per cent. of cases of filariasis. Mikrofilariæ are present in the blood in 36 per cent. (12 out of 33) of cases. _Chyluria._--Exceedingly rare in Fiji. Theory would demand an obstruction above the point of entry of the lacteals, _viz._, the pre-aortic lymphatic glands, but in cases in temperate regions it may occur without any such lesion. In some of these cases the fluid is not chyle (fat absent), but presumably lymph. A discussion of the mode of production of chyluria, lymph scrotum, elephantiasis, etc., is at present premature; theory has far outrun fact. Too much stress had been laid on the mechanical action of the worms to the almost total exclusion of their (or possibly their larval) toxic action. The above analysis has been made in the hope of acquiring more extended observations similar to those made by Bahr. _Geographical Distribution._--_Filaria bancrofti_ is known in nearly all tropical countries. It occurs in India, China, Indo-China, Japan, Australia, Queensland, the Islands of Polynesia (with the exception of the Sandwich Islands), Egypt, Algeria, Tunis, Madagascar, Zanzibar, Sudan, etc., the south of the United States of America, Brazil, the Antilles, etc. Whether it is the same species in all cases is questionable. *Filaria demarquayi*, Manson, 1895. Syn.: _F. ozzardi_, Manson, 1897. [Illustration: FIG. 284.--_F. demarquayi_: tail, showing paired large fleshy papillæ. (After Leiper.)] The adult female _F. demarquayi_ measures from 65 to 80 mm. in length by 0·21 to 0·25 mm. in breadth. The head has a diameter of from 0·09 to 0·1 mm. The mouth is terminal. The genital pore opens at 0·76 mm. from the head. The alimentary canal is nearly straight and terminates in an anus, which is subterminal. The opening of the anus is marked by a slight papilla. The tail is curved. It rapidly diminishes in size just below the anal papilla. A characteristic pair of fleshy papillæ project from the tip of the tail. The diameter near the tip of the tail before its termination is 0·03 mm. _F. demarquayi_ is a thicker worm than _Ac. perstans_. It differs from _F. bancrofti_ in the greater size of the head, in the smaller tail, and particularly in the marked fleshy papillæ at the tip of the tail. These papillæ are knobby, and not simply cuticular as in _Ac. perstans_. The male of _Filaria demarquayi_ has still to be found. The adult female form of _F. demarquayi_ was found by Dr. Galgey in the body of a native of St. Lucia in whose blood the larvæ had been found during life. Five adult females were found in the connective tissue of the mesentery. The larva measures 200 µ in length by 5 µ in breadth; it is sharp-tailed, and has no sheath. Its movements are very active, and the absence of a sheath enables it to glide along freely all over the slide. It observes no periodicity, being present in the peripheral circulation both by day and by night. As a rule, some eight or ten parasites are found in an ordinary preparation. Sometimes hundreds of these larval filariæ may be counted on every slide. The intermediate host has not been discovered. _Geographical Distribution._--St. Vincent, Dominica, Trinidad, and St. Lucia (West Indies), British Guiana, New Guinea (?). [Illustration: FIG. 285.--_Mf. demarquayi_ in thick film, dried and stained with hæmatoxylin. 6, unshrunken; 7, shrunken. × 1,000. (After Fülleborn.)] *Filaria taniguchi*, Penel, 1905. Female 68 by 0·2 mm. in breadth. Cuticle non-striated. Mouth two pairs of papillæ. Anus 23 mm. from extremity. Vulva 1·3 mm. from mouth. Larva 164 µ by 8 µ, sheathed. Tail truncated. Periodicity nocturnal. _Habitat._--Lymphatic glands of man. Japan. *Filaria (?) conjunctivæ*, Addario, 1885. Syn.: _Filaria peritonei hominis_, Babes, 1880; _Filaria inermis_, Grassi, 1887; _Filaria apapillocephata_, Condorelli-Francaviglia, 1892. The female only of this species is known. It measures 16 to 20 cm. in length and 0·5 mm. in breadth, and is of a whitish or brownish tint. The cuticle is striated with fine transverse and more marked longitudinal striæ with the exception of a small field surrounding the mouth, which is terminal and has neither papillæ nor lips. The œsophagus measures 0·6 mm. in length. The anus is 3 mm. in front of the rounded posterior extremity, and behind it there are two (glandular?) sacs. The vulva is close behind the oral aperture; the vagina soon divides into two convoluted uteri, which are filled with eggs and embryos. Embryos 350 µ by 5·5 µ. [Illustration: FIG. 286.--_Filaria_ (?) _conjunctivæ_: to the left, life size; to the right, the anterior extremity magnified. (After Addario.)] This species (115 mm. long) was first observed in Milan by Dubini in the eye of a man; subsequently it was observed, encysted and calcified (190 mm. long), by Babes in the gastro-splenic omentum of a woman in Budapest, and finally one (95 mm. long) was extracted by Vadela from a tumour the size of a pea in the ocular conjunctiva of a woman in Catania (Sicily), which case has been described by Addario. Possibly _Agamofilaria palpebralis_, Pace, 1867 (_nec_ Wilson, 1844), and _A. oculi humani_, v. Nordm., 1832, are the same species. [Illustration: FIG. 287.--_Filaria_ (?) _conjunctivæ_: anterior end greatly magnified; the mouth with the pharynx in the middle; in the cuticle on the right side the opening of the vagina, and behind it the excretory pore. (After Grassi.)] _Filaria_ (?) _conjunctivæ_ is certainly only an incidental parasite of man; the horse and ass are its normal hosts, but it is not common in these animals, or is frequently confused with _Hamularia equi_, Gmelin, 1789. Group. *Agamofilaria*, Stiles, 1906. Not a generic but a group name for immature _Filariidæ_ the development of which does not admit of generic determination. *Agamofilaria georgiana.* Adult unknown, length from 32 to 53 mm. Maximum diameter 560 µ to 640 µ. Head no cephalic cone. Mouth small, circular, surrounded by six papillæ (two small latero-median and four sub-median). The larger papillæ are 24 µ from base to tip. Excretory pore about 0·5 mm. from head. Anus 64 µ to 128 µ from tip. Cuticle fine striæ near anus, occasionally elsewhere. Lateral lines clearly marked. Œsophagus 2·5 to 2·9 mm. Rectum 200 µ long. _Habitat._--Superficial sores on the ankle of a negress, Georgia, U.S.A. *Agamofilaria palpebralis*, Pace, 1867 (_nec_ Wilson, 1844). 100 by 1·5 mm., removed from a cyst in the left upper eyelid of a boy by Pace, in Palermo. *Agamofilaria oculi humani*, v. Nordmann, 1832. Syn.: _Filaria lentis_, Diesing, 1851. The sexless Nematodes observed in the lens of the human eye were termed _Filaria oculi humani_. Only three cases are known. v. Nordmann observed very small round worms in the lens of a man and woman with cataract, and Gescheidt once found three specimens in the lens of a woman similarly affected. The demonstration of nematode-like formations in the vitreous remains uncertain even when movements are observed, and when they cannot be extracted and examined microscopically the doubt may occur that one may have mistaken the remains of the hyaloid artery for a worm, which it resembles in form, size and colour; the slightest movement of the eye also causes it to move so that it simulates a living organism. Accordingly it would be more correct to exclude all the cases known only ophthalmoscopically (Quadri, 1857; Fano, 1868; Schoeler, 1875; Eversbusch, 1891). There then remains only one positive case, described by Kühnt in 1891. In this case it was possible to follow the gradual growth of the parasite for some time, and the worm, which measured only 0·38 mm. in length, was finally extracted. *Agamofilaria labialis*, Pane, 1864. The parasite measures 30 mm. in length; the anterior extremity is pointed; the terminal oral aperture is surrounded by four papillæ; the anus opens 0·5 mm. in front of the posterior extremity; the vulva is 2·5 mm. in front of the anus; the uterus is double; the anterior one passes with convolutions forward to the cephalic end; the posterior one is directed backwards and remains rudimentary. Extracted from a small pustule on the inner surface of the upper lip. Also found in Naples by Pierantoni in 1908. The position of many of these worms is doubtful, and still more so is that of many other imperfectly described “Filariæ,” which are hardly more than useless and confusing names. These include the following:-- *Filaria (?) romanorum-orientalis*, Sarcani, 1888. Observed in the blood of a Roumanian woman; 1 mm. in length, 0·03 mm. in breadth; tail end pointed, a tongue-like appendage on the head. Eggs the size of a red cell with developed embryo, apparently viviparous. *Filaria (?) kilimaræ*, Kolb, 1898. Several female specimens, 10 to 20 cm. long by 0·5 to 1 mm. broad, were once found free in the abdomen of a fallen Kitú warrior; according to Spengel, who examined them, the oral papillæ of these worms were similar to those of _Dracunculus medinensis_. Moreover, Kolb classifies together Nematodes that probably have no connection with each other. *Filaria (?) sp.?* Cholodkowsky calls attention to Filariæ that are still unknown which cause tumours resembling whitlows on the fingers of peasants of the Twer Government. _Mikrofilaria powelli_, Penel, 1905. In Bombay. _Mikrofilaria philippinensis_, Ashburn and Craig, 1906. In the Philippines. Genus. *Setaria*, Viborg, 1795. Syn.: _Hamularia_, Treutler, 1793; _Tentacularia_, Zeder, 1800 (_nec_ Bosc, 1797). Mouth with projecting peribuccal armature deeply notched on the lateral margins, less so dorsally and ventrally. Tail in both sexes with peculiar caudal appendages. Parasitic in serous cavities, especially of ruminants. *Setaria equina*, Abildg., 1789. Syn.: _Gordius equinus_, Abildg., 1789; _Filaria equi_, Gmelin, 1789; _Hamularia lymphatica_, Treutler, 1793; _Tentacularia subcompressa_, Zedder, 1800; _Filaria papillosa_, Rud., 1802; _Filaria hominis bronchialis_, Rud., 1819; _Filaria hominis_, Dies., 1851; _Strongylus bronchialis_, Cobb., 1879. The body is whitish, filiform, pointed posteriorly. The cuticle presents a delicate transverse striation. The mouth is small, round, and surrounded by a chitinous ring, the border of which carries, at the sides, two semilunar lips, and there is on the dorsal as well as on the ventral surface a papilliform process; on the tail, corresponding with each sub-median line, is a conical papilla. The male measures 6 to 8 cm. in length; the posterior extremity ends in a corkscrew spiral; there are on each side four pairs of pre-anal and four or five post-anal papillæ; the spicules are unequal. The female measures 9 to 12 cm. in length and is viviparous; the embryos measure 0·28 mm. in length and 0·007 mm. in breadth. [Illustration: FIG. 288.--_Setaria equina_: left, male; right, female. Natural size. (After Railliet.)] [Illustration: FIG. 289.--_Setaria equina_: anterior end, magnified. (After Railliet.)] _Setaria equina_ is a frequent parasite of horses and asses; it inhabits the peritoneal cavity, and from there occasionally invades the female genitalia or even the liver; it is found more rarely in the pleural cavity or in the cranium. The statement that it also occurs in the subcutaneous connective tissue is probably due to confusion with _Setaria_ (_Filaria_) _hæmorrhagica_, Raill., 1885 (_Filaria multipapillosa_, Cond. et Drouilly, 1878). _Setaria labiata papillosa_ (immature form) occurs in the eye of the horse, adults in the peritoneal cavity. Treutler, in 1790, found a filaria in the enlarged bronchial lymphatic gland of a patient suffering from phthisis. It measured 26 mm. in length and had two spicules, which Treutler mistook for mouth hooks, hence the name _Hamularia_. Blanchard mentions another case from Geneva, Brera a third and v. Linstow a fourth. As shown by the synonyms, a few authors consider this form to be a distinct species, which is hardly probable. Genus. *Loa*, Stiles, 1905. Characterized by the possession of cuticular bosses in both sexes (fig. 294). *Loa loa*, Guyot, 1778. Syn.: _Filaria oculi_, Gerv. et v. Ben., 1859; _Dracunculus oculi_, Diesing, 1860; _Dracunculus loa_, Cobbold, 1864; _Filaria subconjunctivalis_, Guyon, 1864. The male measures 25 to 35 mm. in length, and 0·3 to 0·4 mm. in breadth; the cuticle is not striated, but, with the exception of the anterior and posterior extremities (1·5 mm.), is beset with numerous irregularly distributed bosses (4 µ to 12 µ high by 12 µ to 27 µ broad). The anterior extremity is somewhat attenuated, and in front is conical and transversely truncated. At the anterior limit of the conical part is a small papilla corresponding with the dorsal and ventral median lines, and a little in front six non-projecting sensory papillæ (two lateral, four sub-median). Excretory pore 0·65 mm. from the anterior end. The posterior extremity is attenuated and somewhat curved ventrally; the anus is 0·082 mm. distant from the rounded posterior border. In front of the anus on each side are three globular and pedunculated papillæ of different sizes, set close one behind the other but asymmetrically; behind the anus on either side are two smaller papillæ of a different shape; the anterior one resembles the pre-anal papillæ in form, but is smaller; the posterior one is conical, and rests with a broad base on the cuticle. The spicules are 0·113 and 0·176 mm. long. The female measures 45 to 63 mm. in length by 0·5 mm. in breadth. It is also beset with irregularly distributed bosses, which in places lie close to each other, and extend to the anterior extremity; posteriorly they become less frequent, but are not entirely absent. The anterior extremity is conical, the posterior one straight, attenuated, rounded off, 0·17 mm. from the anus. The uteri contain eggs in the most various stages of development, as well as hatched-out larvæ, 253 µ to 262 µ in length and 4·7 µ to 5 µ in breadth. The vulva lies about 2 mm. from the head end. The vagina, 9 mm. long, divides into two branches, which at first run posteriorly and parallel to one another for about 18 mm. One then bends forward, runs as far as the œsophagus, bends here again and runs backward to end at the point of its first bending. The other branch at first runs straight backward and then bends forward, but before reaching the point of the first bend of the anterior tube bends backward again, forms again a loop and ends at the level of the anus. The tubes consist in the main of the uterus, then a club-shaped swelling, the receptaculum seminis, then the oviduct 2 mm. long, and finally the ovary. [Illustration: FIG. 290.--_Loa loa_: the anterior end of the male, magnified. (After R. Blanchard.)] [Illustration: FIG. 291.--_Loa loa_: anterior portion of the female as far as vulva. (After Looss.)] [Illustration: FIG. 292.--_Loa loa_ in situ. Natural size. (After Fülleborn and Rodenwaldt.)] [Illustration: FIG. 293.--_Loa loa_: male on the left, female on the right. × 2. (After Looss.)] Unsegmented eggs measure 32 µ by 17 µ, in the morula stage 40 µ by 25 µ, and when containing embryos 50 µ by 25 µ. The vitelline “shell” of the egg is, according to most authors, stretched by the embryo and becomes the sheath of the hatched larva. While still in the vulva, the larva measures 217 µ to 274 µ (average 246 µ) in fresh, 146 to 226 µ (average 192 µ) stained. [Illustration: FIG. 294.--_Loa loa_: on the left, the hind end of a male; on the right, of a female. Note the cuticular bosses shown in the figure of the female. × 285. (After Looss.)] [Illustration: FIG. 295.--_Loa loa_: lateral view of tail of male showing papillæ. (After Lane and Leiper.)] [Illustration: FIG. 296.--_Loa loa._ _a_, ventro-lateral aspect of tail showing papillæ and one spicule; _b_ and _c_, terminations of the two spicules. (After Leiper.)] _Site of Worms._--In various localities; under the muscular aponeuroses on extensor surfaces of arms and legs, fingers, trunk, eyelid, conjunctiva, frænum linguæ, penis, pericardium, anterior chamber of eye, and, according to some authorities, in lymphatic vessels, _e.g._, those of spermatic cord. As many as thirty adults may be found. The worms appear to be frequently immature, and it has been stated that worms in superficial parts are immature, those situated deeply are mature, but the data are few. The first accounts of _Loa loa_--long since forgotten--were reported by Pigafetta, and are contained in a book of travels on the Congo printed in 1598. In an accompanying illustration is depicted, not only the ancient method of extraction of the Medina worm, but also the operative removal of the filaria from the conjunctiva. Subsequently the presence of the worm in negroes was confirmed by Bajon in Guiana (1768) and by Mongin in Mariborou (San Domingo), likewise in a negro (1770). At about this time a French ship’s doctor, Guyot, was cruising on the West Coast of Africa; he observed the parasite termed “loa” by the natives, and learned that it was frequent in the negroes of the Congo district. Since that time numerous observations have been reported. It was formerly common in South America, where the parasite was imported by slaves, but it disappeared when the traffic ceased; it was particularly prevalent in the Congo, where it occurs not only in natives, but also in Europeans. During recent times it has repeatedly been observed in Europe in negroes as well as in white men who have lived on the West Coast of Africa. Nematodes of different size have been repeatedly observed in the eye of man, in the anterior chamber, lens and vitreous. For example, Mercier, in 1771 and 1774, removed a filaria out of the anterior chamber of two negroes in St. Domingo. One was 36 mm. long. Barkan, in 1876, in San Francisco, removed one from the eye of an Australian. Again, Cappez and Lacompte, in Brussels, in 1894, observed for some weeks immature Nematodes in the eye of a negro girl, aged 2-1/2 years, and then removed them. What these Nematodes actually were in these cases it is impossible to say. _Structure of Larvæ._--In dried films the larva varies in size from 140·5 µ to 166·5 µ, average, 152·5 µ; while another set of measurements gave the values 131 µ, to 150 µ, average, 143·6. In films fixed with hot alcohol the dimensions were 208 µ to 254 µ, average, 231 µ. The nerve ring 21·4 to 21·8 per cent. Excretory pore 30·4 to 31·8 per cent. Excretory cell 34·8 to 37·3 per cent. G1 cell 68·2 to 68·5 per cent. Anal pore 81·6 to 82·4 per cent. of total length. For other details _cf._ _Filaria bancrofti_. _Larvæ in Blood._--These from their diurnal periodicity are known as _Mikrofilaria diurna_. The evidence that these larvæ are the young of the adult worm _Loa loa_ is: (1) They are identical in structure with larvæ taken from the uterus of _L. loa_; (2) their geographical distribution is the same as that of _L. loa_; (3) they eventually occur in the blood of patients suffering from Calabar swellings, a condition due to _L. loa_. Their occurrence in the blood in this latter condition and in _L. loa_ infections we shall consider later. _Periodicity._--Here, as in the case of the larvæ of _Filaria bancrofti_, the larvæ that appear in the blood are probably the overflow simply of the larvæ which we assume, on analogy, to have their principal site in the lungs. They appear in the blood about the time of getting up, 6 to 8 a.m. (10 in 20 mm.^3), at 12 noon there are twenty-four, at 8 p.m. the number has fallen to eighteen, and at midnight to one, while from 2 a.m. to 6 a.m. none, or one only, may be found. This periodicity is, as a rule, a very constant one, but there are exceptions, and in certain cases more have been found at midnight than at 9 a.m. The periodicity is also lost in pathological conditions, _e.g._, sleeping sickness (_vide_ also under _Filaria bancrofti_). The possibility of non-periodic _Loa loa_ larvæ should also be considered. [Illustration: FIG. 297.--_Mf. loa_: in thick film, dried and stained with hæmatoxylin. × 1,000. (After Fülleborn.)] _Pathology._--The parasite wanders about the body, and may be seen under the skin in thin parts. Their advance is in some cases at the rate of an inch in two minutes. During their progress they give rise to creeping sensations and to a condition of transient œdematous areas known as Calabar swellings on various parts of the body, _e.g._, arm. These vary in diameter from 1 to 10 cm., and often shift their position an inch or so a day. They give rise to a certain amount of redness, tension and heat, and their development is promoted by muscular action of the part. They disappear to reappear elsewhere. The condition is associated with a high eosinophilia, 50 per cent. being not uncommon. Patients known to harbour _L. loa_, _e.g._, native children, frequently show no larvæ in their blood, but they may do so after years of infection. Again, in patients having an infection of _Mikrofilaria diurna_, there is frequently at the time no evidence of the presence of _Loa loa_ adults. Here again they may appear later, but the conditions which determine whether persons infected with _L. loa_ show larvæ in the blood, or persons infected with _Mikrofilaria diurna_ also show _L. loa_, are unknown, though explanations unsupported by facts abound. Likewise also the mode of production of the swellings is unknown. Not uncommonly _Mikrofilaria perstans_ occurs in the blood together with _M. diurna_. _Duration of Life._--This is long, as some cases have been observed five to six years after leaving Africa. The incubation period is about a year. _Life-history._--Development of the larvæ takes place in the salivary glands of Chrysops sp. as shown by Leiper. _Geographical Distribution._-- West Africa, especially in Congo. Genus. *Acanthocheilonema*, Cobbold, 1870. Cuticle striated _longitudinally_. Œsophagus divided into two portions. Tail in both sexes with short lateral conical cuticular appendages. Spicules unequal, the larger membranous distally, the smaller hooked. Vulva in œsophageal region. *Acanthocheilonema perstans*, Manson, 1891. Syn.: _Filaria perstans_, P. Manson, 1891; _Filaria sanguinis hominis_ var. _minor_, Manson, 1891. [Illustration: FIG. 298.--_Acanthocheilonema perstans._ 1, tail of male; 2, tail showing cuticular flaps devoid of fleshy contents. (After Leiper.)] The adult female _Ac. perstans_ measures 70 to 80 mm. in length by 120 µ to 140 µ in breadth. The head is club-shaped and measures 0·07 mm. in diameter. The vulva opens at 0·6 to 1·0 mm. from the head. The tail is curved and presents a cuticular thickening which forms two triangular appendages. The anus opens at the apex of a papilla situated in the concavity of the curve formed by the tail 150 µ from the end. The diameter of the tail just before termination is 0·02 mm. [Illustration: FIG. 299.--_Mf. perstans_ in thick film, dried and stained with hæmatoxylin; 4, unshrunken; 5, shrunken. × 1,000. (After Fülleborn.)] The adult male measures 45 mm. in length by 60 µ to 80 µ in breadth. The diameter of the head is 0·04 mm. The tail is much curved. There are four pairs of pre-anal papillæ and two pairs of post-anal papillæ. Spicules very unequal in size. Cloaca 121 µ from the tail end. At the tail end two triangular cuticular appendages. The adult worms inhabit the connective tissue at the base of the mesentery, especially in the region of the pancreas, abdominal aorta and suprarenals. To find them the mesentery should be removed, placed in a 2 per cent. solution of formalin, and then carefully examined at leisure. _Mikrofilaria perstans._--160 µ to 210 µ by 5 µ to 6 µ broad. Has no sheath. Cuticle transversely striated. Tail rounded off, not pointed. Nerve ring at 34 µ. Excretory pore 49 µ, genital pore 125 µ from head. Smaller larvæ 90 µ to 110 µ by 4 µ broad. A “fang” is also described on the head. _Mf. perstans._ _Mf. demarquayi._ (1) Tail stumpy. (1) Tail pointed. (2) Column of nuclei extends to (2) Does not extend to tip. tip of tail. _Periodicity._--None. _Life-history._--Unknown. _Geographical Distribution._--Very common in many parts of Africa: Sierra Leone, Dahomey, Northern Nigeria, Southern Nigeria, Cameroons, Ivory Coast, Gold Coast, Old Calabar, Congo, Uganda. Absent from Zululand, Basutoland. On the East Coast of Africa it is not found in the towns of Zanzibar and Mombasa, neither is it found in the country of the Masi, nor amongst the Kavirondo, who dwell along the north-east shores of Lake Victoria. In South America, _Ac. perstans_ is very common amongst the aboriginal Indians in the interior of British Guiana. However, it is not found in Georgetown and in New Amsterdam, neither is it found in the cultivated strip of coast lying between these two towns, but it is common on the coast farther north near the Venezuelan boundary, where the forests stretch to the sea. The Waran Indians, who live at the mouth of the Waini river, harbour this parasite. It is absent in the West Indies. Topographically, _Ac. perstans_ is found only in areas covered by dense forest growth and abounding in swamps. In Kavirondo, where the forest disappears and the land is covered with scrub and short grass, it is not found; likewise it is not found on the grassy plains of the highlands of British East Africa. Towns and cultivated areas are free from it. Genus. *Dirofilaria.* Railliet and Henry, 1911. Body very long, thread-like, cuticle transversely striated. Mouth with six papillæ. Male tail spiral with voluminous pre-anal and some large post-anal papillæ; spicules unequal. Vulva near the anterior hundredth of body; viviparous. Parasitic in heart or blood-vessels and subcutaneous tissue. *Dirofilaria magalhãesi*, R. Blanchard, 1895. Syn.: _Filaria bancrofti_, v. Linstow, 1892; _Filaria bancrofti_, P. S. de Magalhães, 1892 (_nec_ Cobbold, 1877). The male measures 83 mm. in length by 0·28 to 0·40 mm. in breadth. The anterior extremity is rounded, and has no papillæ (?6); the posterior extremity exhibits a double curve, with four pre-anal and four post-anal papillæ on each side. These are large and have a villous appearance. The mouth is round and unarmed, the pharynx measures 1 mm. in length, is cylindrical, very muscular, and its hinder part is dilated. The anus is situated 0·11 mm. in front of the hind end. There are probably two unequal spicules; one only, however, is known--apparently the shorter one--the length of which is given as 0·17 to 0·23 mm. [Illustration: FIG. 300.--_Dirofilaria magalhãesi_: posterior extremity. (After v. Linstow.)] The female measures 155 mm. in length and 0·6 to 0·8 mm. in breadth; the rings of the cuticle are 0·005 mm. apart (in the male 0·003 mm. apart); the anterior extremity is slightly thickened and club-like, the posterior extremity is slender, and terminates obtusely; the lateral line is 0·127 mm. in breadth (that of the male 0·007 to 0·008 mm.); the anus opens 0·13 mm. in front of the hind end, the vulva is 2·5 mm. distant from the mouth, the ovaries are two much convoluted tubes. The eggs measure 38 µ by 11 µ. This species was first discovered at a _post-mortem_, in the left ventricle, by J. P. Figueira de Saboia in Rio de Janeiro, and has been described by P. S. de Magalhães. _D. immitis_ occurs in the right ventricle of the heart of the dog in Europe and the Tropics. _D. repens_ is also a common subcutaneous Nematode in dogs in Annam. Sub-family. *Onchocercinæ*, Leiper, 1911. Cuticle with spiral thickenings. Genus. *Onchocerca*, Diesing, 1841. Male with four pre-anal papillæ. Female with vulva situated anteriorly. *Onchocerca volvulus*, R. Leuckart, 1893. Syn.: _Filaria volvulus_, R. Leuckart, 1893. The adult male measures 30 to 35 mm. in length by 0·14 mm. in breadth. The body is white, filiform, attenuated at both ends. The head is rounded and has a diameter of 0·048 mm. The cuticle is distinctly transversely striated. The mouth is unarmed. The alimentary canal is straight, the anus opening 0·07 mm. from the tip of the tail. The tail is strongly curved and somewhat flattened on the concave surface. There are three papillæ, one large and two small, on each side of the cloaca and one large and two post-anal small papillæ. Two curved spicules, 0·166 and 0·08 mm. respectively. The adult female is of uncertain length, but much longer than the male, probably about 10 to 12 cm. The head is rounded and truncated; it measures 0·065 mm. in diameter. The tail is curved. The vulva opens 0·55 mm. from the head. The hand-like cuticular thickenings are well marked. Eggs ovoid with a prolongation at each pole “like an orange wrapped in tissue paper.” The larva measures about 300 µ by 7 µ to 8 µ; it has no “sheath.” The body tapers from about the last fifth of its length, and terminates in a sharply pointed tail. At about the anterior fifth of the body there is a *V* spot. _O. volvulus_ is found in peculiar subcutaneous tumours, the size of a pea to that of a pigeon’s egg. The same patient may present one or several of these tumours. The regions of the body most frequently affected are those in which the peripheral lymphatics converge. Thus they are usually found in the axilla, in the popliteal space, about the elbow, in the sub-occipital region and in the intercostal spaces. The tumours are never adherent to the surrounding structures, and can be easily enucleated. They are formed of a dense connective tissue wall and internally a looser fibrous meshwork. This is traversed by a series of canals in which the worms lie, but they are also partly embedded in the denser wall. The canals apparently dilate into cavities filled with slimy pus-like fluid consisting largely of larvæ. According to Brumpt the posterior extremity of the male, and the anterior extremity of the female with its vaginal opening, are free in one of the spaces for the purpose of copulation and parturition. If a tumour be cut into and placed in salt solution, Rodenwaldt states that the undamaged males wander out into the solution. The formation of the tumours is elucidated by Labadie-Lagrave and Deguy’s case. The authors found an immature female _Onchocerca volvulus_ in a lymphatic vessel partly obstructed by an infiltration of fibrin and leucocytes. It appears, therefore, that the presence of the parasites within the lymphatics gives rise to an inflammatory process, and that the consequent fibrinous deposit envelops the parasites, obliterates the lumen of the vessel, and ultimately isolates the affected tract. At any rate, in young tumours the worms appear to lie in a structureless substance permeated by leucocytes in which connective tissue is gradually organized from the periphery, thus isolating the worms. In cases of infection with _O. volvulus_ larvæ have been found by Ouizilleau, Fülleborn, and Simon in lymph glands, and in the finger blood if considerable pressure is used so as to squeeze lymph out of the tissues. They are _sheathless_, and the following are the dimensions in ordinary dried films: Length, 274 µ; nerve ring, 23·7 per cent.; G1 cell, 69·6 per cent.; end of last tail cell, 96·3 per cent. The dimensions of larvæ of _O. volvulus_ taken from the uterus and prepared in the same way are: Length, 224·5 µ; nerve ring, 24·3 per cent.; G1 cell, 68·9 per cent.; end of the last tail cell, 95·5 per cent. In all probability the larvæ in the glands and blood are those of _O. volvulus_. According to the natives, the tumours may last indefinitely and never ulcerate. Some old patients told Brumpt that their tumours had been present since childhood. Probably _Onchocerca volvulus_, like some other _Filariidæ_, may live for many years. _O. volvulus_ occurs in various parts of West Africa: Gold Coast, Sierra Leone, Dahomey, Lagos, Cameroons. Brumpt, on the banks of the Welle between Dongon and M’Binia (Belgian Congo), found about 5 per cent. of the riverine population affected. Family. *Trichinellidæ*, Stiles and Crane, 1910. Sub-family. *Trichurinæ*, Ransom, 1911. Male with a single long spicule, with sleeve-like sheath. One ovary. Eggs with an opening at each pole closed by a plug-like operculum. Eggs hatch on being swallowed by a new host. Genera: Trichuris, Capillaria. Genus. *Trichuris*, Röderer and Wagler, 1761. Syn.: _Trichocephalus_, Goeze, 1782 (_nec Trichiurus_, L., 1758); _Mastigodes_, Zeder, 1803. The anterior part of the body is very long and thread-like; the posterior, much shorter part, is thicker, rounded posteriorly, and the anus is terminal. The males have the posterior extremity spirally rolled; the vulva is situated at the commencement of the posterior part of the body. The Trichocephali live in the large intestine of mammals, the cæcum by predilection; their development is direct, infection occurs through the ingestion of embryo-containing eggs. *Trichuris trichiura*, Linnæus, 1761. Syn.: _Trichocephalus trichiurus_, L., 1771; _Ascaris trichiura_, L., 1771; _Trichocephalus hominis_, Schrank, 1788; _Trichocephalus dispar_, Rud., 1801. The male measures 40 to 45 mm. in length, the spicule is 2·5 mm. long, its retractile sheath is beset with spines. The female measures 45 to 50 mm. in length, of which two-fifths appertain to the posterior part of the body. The ova are barrel-shaped and have a thick brownish shell which is perforated at the poles. Each opening is closed by a light-coloured plug. The eggs measure 50 µ to 54 µ in length and 23 µ in breadth; they are deposited before segmentation. _Trichuris trichiura_ usually lives in the cæcum of man, and is also occasionally found in the vermiform appendix and in the colon, exceptionally also in the small intestine; usually only a few specimens are present, and these do not cause any particular disturbance, although, as Askanazy found, they feed on blood; in other cases cerebral symptoms of more or less severity are observed when Trichocephali are present in large numbers. At _post-mortems_ performed soon after death the filiform anterior extremity of the worm is frequently found embedded in the mucous membrane (Askanazy). [Illustration: FIG. 301.--_Trichuris trichiura_: on the left, male; on the right, female with the anterior extremity embedded in the mucous membrane of the intestine; below, egg.] The whip worm is one of the most common parasites of man and appears to be distributed over the entire surface of the globe; it is, however, more frequent in the warmer regions. It is found in persons of both sexes and all ages with the exception of infants. In autopsies it is found in the following numbers: In Dresden in 2·5 per cent., in Erlangen in 11·1 per cent., in Kiel in 31·8 per cent., in Munich in 9·3 per cent., in Petrograd in 0·18 per cent., in Göttingen in 46·1 per cent., in Basle in 23·7 per cent., in Greenwich in 68 per cent., in Dublin in 89 per cent., in Paris in about 50 per cent., and in Southern Italy in almost 100 per cent. On examining the fæces the eggs of the whip worm were found as follows: In Munich in 8·26 per cent., in Kiel in 45·2 per cent., in Greifswald in 45 per cent., in North Holland in 7 per cent., in Novgorod in 26·4 per cent., in Petrograd in 5 per cent., in Moscow in 5·3 per cent. The development of the eggs is completed in water or in moist soil, and occupies a longer or shorter time according to the season; the eggs possess great powers of resistance, as do the larvæ, which, according to Davaine, may remain as long as five years in the eggshell without losing their vitality. Leuckart proved by experiment that direct infection with _Trichuris ovis_ (_Ovis aries_) and _T. crenata_ (_Sus scrofa dom._) was produced by embryo-containing eggs; Railliet obtained the same results with _T. depressiuscula_ of dogs, and Grassi subsequently, by means of two experiments, demonstrated the direct development of _Trichuris trichiura_. In one case embryo-containing eggs were swallowed on June 27, 1884, and on July 24 the ova of Trichocephali were found in the fæces for the first time. _Trichuris trichiura_ is found not only in man, but also in various monkeys (_T. palæformis_, Rud.), as well as in lemurs (_T. lemuris_, Rud.). Other species are _T. crenata_ in pig; _T. ovis_ in cattle, sheep, goat, and pig (?); _T. depressiuscula_ in dog; _T. campanula_ in cat; _T. unguiculata_ in rabbit and hare; _T. cameli_ in camel; _T. discolor_ in humped cattle; _T. nodosus_ in mouse; _T. alcocki_ in the thamin (India); _T. globulosa_ in camel; _T. giraffæ_ in giraffe. Sub-family. *Trichinellinæ*, Ransom, 1911. Male without spicule; females ovoviviparous. Larvæ penetrate muscles of host and become encysted. Genus: Trichinella. Genus. *Trichinella*, Railliet, 1895. Syn.: _Trichina_, Owen, 1835 (_nec_ Meigen, 1830). Very small _Trichinellinæ_, the males of which have two conical appendages at the caudal extremity; the vulva is situated at the border of the anterior fifth of the body. There is only one species. *Trichinella spiralis*, Owen, 1835. Syn.: _Trichina spiralis_, Owen, 1835. The male measures 1·4 to 1·6 mm. in length and 0·04 mm. in diameter. The anterior part of the body is narrowed, the orifice of the cloaca is terminal and lies between the two caudal appendages; internal to these are two pairs of papillæ, dorsal one behind the other. The cloaca is evertible for copulation. The females measure 3 to 4 mm. in length and 0·06 mm. in diameter; anus terminal. _Trichinella spiralis_ in its adult stage inhabits the small intestine of man, pig, wild boar, rat. The young do not leave the body of the host but become encysted in the muscles. Experimentally it develops in the black rat (_Mus rattus_), the sewer rat (_M. decumanus_), the domestic pig (_Sus scrofa dom._), the wild boar (_Sus scrofa ferox_), the domestic dog (_Canis familiaris_), the fox (_C. vulpes_) the badger (_Meles taxus_), the polecat (_Putorius fœtidus_), the marten (_Mustela foina_), the raccoon (_Procyon lotor_), the hippopotamus and the cat, and many other mammals (rodents and carnivora); Trichinellæ have been artificially introduced, by administering the encysted stage, into the dog, the mole (_Talpa europæa_), the mouse (_Mus musculus_), the hare (_Lepus timidus_), the rabbit (_L. cuniculus_), the hedgehog (_Erinaceus europæus_), the marmot (_Cricetus vulgaris_), the vole, the dormouse, the sheep, the calf, the horse, etc. Human beings and the pig, rat, mouse, guinea-pig and rabbit are most easily infected; less easily the sheep, calf and horse; with difficulty the cat, dog and badger. Trichinella can also be reared in birds (fowl, pigeon and duck), but the young do not encyst in the muscular system, but are expelled with the fæces. By cold-blooded animals as well as by insects (_Calliphora vomitaria_), encysted Trichinellæ are evacuated without undergoing any change, but they will still develop if subsequently ingested, say, by rabbits. According to Gujon, however, Trichinella can develop in salamanders, because he has found Trichinella of the muscles in these animals after they had been fed on encysted specimens. A high temperature (30°C.) must be provided in which to keep the experimental animals to ensure the success of the infection. [Illustration: FIG. 302.--_Trichinella spiralis_. ♀, mature female: _E_, embryos; _V_, vulva; _Ov_, ovary. ♂, mature male: _T_, testes. _c._, newly born larva. _d._, larva in the muscles. _e._, encapsuled larva in the muscles. Magnified. (After Claus.)] _History._--Encapsuled Trichinellæ had been observed in London by Peacock (1828) and by J. Hilton (1833) in the muscular system of man; soon after (1835), Paget found them in London in an Italian who had died of tuberculosis, and recognized them to be encysted entozoa, which R. Owen described as _Trichina spiralis_. Soon after, some further observations were reported on the occurrence of encysted Trichinellæ, in man, in England, Berlin, Heidelberg, Denmark, North America; they were also found in the pig (Leidy, Philadelphia) and the cat (Herbst, Göttingen, and Gurlt, Berlin). Herbst even succeeded in infecting a badger with encysted Trichinellæ, and subsequently infected two dogs with the flesh of this badger (1850). In 1855 R. Leuckart (Giessen) also commenced feeding experiments, and, like Küchenmeister and Virchow (1859), first went on the wrong track because it was believed at that time that Trichinellæ were the larvæ either of Trichocephalus or Strongylus. Nevertheless, these experiments yielded some important results; they showed that Trichinellæ become adult in the intestine within a few days, and that the females are viviparous (Leuckart). Until that time Trichinellæ had been regarded as fairly harmless guests of man, but opinions soon changed when Zenker in Dresden (January, 1860), in performing the autopsy of a girl, aged 10, who had entered the hospital with typhoid symptoms and there died, found Trichinellæ (not yet encysted) in the muscles; the intestinal lesions characteristic of typhoid were lacking, but numerous adult Trichinellæ were found in the intestine. Inquiries elicited the fact that at about Christmas time the girl had been taken ill after eating pork, and at the same time the butcher from whom the meat was bought as well as several of his customers fell sick: the pickled pieces of the same meat were full of Trichinellæ. In the face of this information it was not difficult to ascertain the cause of the disease and the manner of infection in Zenker’s case, and it was not long before Leuckart, Virchow and Zenker were able by renewed experiments to demonstrate the cycle of development of _Trichinella spiralis_. Similar investigations followed by Claus in Würzburg, Davaine in Paris, Fuchs and Pagenstecher in Heidelberg, etc. Hardly had Zenker’s case been published than numerous observations on trichinosis in man appeared, some referring to isolated cases, others to small or great epidemics, and nearly all from North Germany. The worst epidemic was that of Hadersleben (1865), in which place, numbering hardly 2,000 inhabitants, 337 persons were taken ill within a short time, and of these 101 died. The source of infection proved to be a single pig, the flesh of which had been mixed with that of three other pigs; 200 of the badly infected persons had exclusively eaten raw pork. Moreover, it soon became clear that epidemics of trichinosis had been observed in Germany prior to 1860, but that their nature had not been recognized, although in a few cases Trichinellæ had been found in the muscles of those who had succumbed. HISTORY OF THE DEVELOPMENT OF _Trichinella spiralis_. Shortly after their introduction into the intestine of experimental animals the encysted Trichinellæ escape from their capsules, which are destroyed by the gastric juices, and they then enter the duodenum and jejunum, where they become adult. During this period they do not grow much, the males from 0·8 to 1·0 to 1·2 to 1·5 mm.; the females to 1·5 to 1·8 mm. Soon after copulation, which takes place in the course of two days, the males die; the females, which during the following days attain a length of 3 to 3·5 mm., either bore more or less deeply into the villi or, by means of Lieberkühn’s glands, into the mucous membrane (Askanazy, Cerfontaine, Geisse), and thus usually attain the lymph spaces. A few also pierce the intestinal wall and are then found in the mesentery and glands. The females deposit their young, the number of which, according to Leuckart, averages at least 1,500, in the lymph spaces; the newly born larvæ measure 90 µ to 100 µ in length, 6 µ in diameter, and they do not appear to increase in size during their migrations. The migrations are mostly passive, that is to say, the larvæ are carried along mainly by the lymph stream to the heart, but sometimes they are active, as may be inferred from the fact that young Trichinellæ are found in various parts of the intestinal wall beyond the chyle and lymph spaces, as well as in abundance in the abdominal cavity. Trichinellæ occur in the heart’s blood of artificially infected animals seven to twenty-three days after infection. If scanty, dilute the blood with about ten times the amount of 3 per cent. acetic acid and centrifugalize. The young brood is distributed from the heart throughout the entire body, but the conditions necessary to its further development are found only in striated muscle; the young Nematodes penetrate the capillaries, attain the intramuscular connective tissue and then invade the fibres (Virchow, Leuckart, Graham[304]). On the ninth or tenth day after infection the first Trichinellæ have reached their destination; but further invasions are constantly taking place because the intestinal Trichinellæ live from five to seven weeks, and continue to produce their young. [304] Trichinellæ that are unable to penetrate into muscular fibres invariably die, no matter where else they settle; their occurrence in the adipose tissue is disputed, but is still possibly correct, as bundles of muscles are present in the fat of bacon. The Trichinellæ do not settle in heart muscle, although they may reach it in cases of heavy infection; they then die or wander into the pericardium, and eventually into the heart cavities. _Symptoms._--(1) Period of invasion: Gastro-intestinal symptoms--nausea, vomiting, watery diarrhœa, colic. Muscular pains may occur even at this period. Recurrent abdominal pains about the eighth day, a _temporary_ œdema. Embryos are abundant in the serous cavities. (2) Period of dissemination: Second week. Myositis, variable in amount, is the predominant symptom. The biceps and calf may be hard and tender. Mastication, speech, respiration, etc., may be difficult and painful. Dyspnœa may be intense. Temperature 104° to 105° F. (3) Period of encystment: Symptoms of marked cachexia. Third week: Second period of œdema, especially of face. Delirium, somnolence, lung affections. Death or gradual subsidence of symptoms in mild cases. Eosinophilia (50 per cent. or more) is present. In consequence of the new batches of young produced during several weeks, the above-mentioned symptoms of disease are often considerably aggravated; the fever increases, delirium may arise, and infiltration of the lungs, fatty degeneration of the liver and inflammation of the kidneys may ensue; the initial slight œdema may extend, the strength dwindles, and in many cases the patients succumb to the trichinosis. In severe cases improvement of the condition is only apt to occur in the fourth or fifth week; the convalescence is always protracted. [Illustration: FIG. 303.--_A._, isolated muscular fibre of a rat, invaded by Trichinella. 510/1. _B._, section through the muscle of a rat; the infected fibre has lost its transverse striation; its nuclei are enlarged and multiplied. 310/1. _C._, portion of a Trichinella capsule, at the pole of which connective tissue cells are penetrating the thickened sarcolemma. (After Hertwig-Graham.)] The muscular fibres attacked degenerate, the transverse striation at first disappearing; the fibres then assume a granular appearance, the nuclei multiply and become enlarged, and are surrounded by an area of granular material, which stains more deeply than the remaining contents of the sarcolemma. Two or three weeks after infection, the spirally rolled-up Trichinellæ have grown to 0·8 to 1·0 mm., and in their vicinity the muscular fibre is swollen, spindle-shaped, and the sarcolemma is glassy and thickened. The inflammation also extends to contiguous fibres, especially to the intramuscular tissue, which proliferates greatly, especially in the vicinity of the degenerated fibres. While the latter become more and more absorbed, the capsule is formed by the inflamed connective tissue, which, penetrating into the glassy and thickened sarcolemma from the poles of the spindle, forms the cystic membrane. According to other authorities, the larvæ settle in the _inter_muscular connective tissue which forms the cyst and not in the muscular fibres within the sarcolemma. The cysts are lemon-shaped and usually lie with their longitudinal axis in the direction of the muscular fibres; on an average they measure 400 µ in length by 250 µ in breadth. Later on fat cells appear at their poles, and after about six or nine months they commence to calcify, the process starting at the poles (fig. 305). Finally, sometimes after the lapse of years, the captive Trichinellæ themselves become calcified. [Illustration: FIG. 304.--Calcified Trichinella in the muscular system of a pig; the capsules are not calcified. (After Ostertag.)] [Illustration: FIG. 305.--Various phases of the calcification of Trichinella of the muscles, which starts at the poles of the capsule.] According to experience, Trichinellæ are not evenly distributed in the muscular system of pigs; the diaphragm, the muscles of the larynx, tongue, abdomen and intercostal spaces are their favourite positions; this predilection for the respiratory muscles is explained by their regular contractions, owing to which regular narrowings of the capillaries take place, thus favouring the settling of the circulating Trichinellæ. The same circumstance probably explains the frequency of the parasites in the tongue. Possibly also the Trichinellæ that bore direct through the intestine may, from the abdominal cavity, penetrate the muscles in the vicinity. Frequently also encysted Trichinellæ are found in remarkable numbers in the vicinity of the points of insertion of the tendons, this proclivity being probably connected with the fact that the Trichinellæ first of all wander into the muscular fibres and find a natural barrier at the points of insertion of the tendons. The Trichinellæ, in their encysted condition, may remain alive and capable of development for many years--in the pig eleven years and in man as much as twenty-five to thirty-one years. Encystment, however, is not a necessary condition for the development of the brood, that is to say, Trichinellæ which reach the gut of suitable animals become sexually mature and multiply provided that they have developed so far as to possess a rudimentary genital spot, which occurs when the body is 0·5 to 0·75 mm. long, but all the same a great part of non-encapsuled Trichinæ perish on their passage through the stomach. The black rat (_Mus rattus_), and more particularly the sewer rat (_Mus decumanus_[305]), are the normal hosts of _Trichinella spiralis_. These animals, especially the last-named species, infect themselves very easily, as they are cannibalistic, and they also transmit trichinosis to other species by which they are devoured, such as pigs, dogs, cats, foxes, bears and martens. Rats are infected also by the ingestion of fæcal matter from infected animals which contains trichinæ (Höyberg). Man becomes infected with Trichinella by eating the flesh, insufficiently cooked, of infected pigs, also, but more rarely, by eating the infected flesh of wild boars, dogs, cats, bears and foxes. [305] It is still a matter of dispute and can hardly be definitely settled whether Trichinellæ were brought to Europe by the sewer rats which invaded Europe at the end of the eighteenth century, or whether they were imported with the Chinese pig in 1820 or 1830, when it was introduced into England and Germany to cross with the native breeds, or whether finally Trichinellæ are also indigenous to Europe. The infection of pigs may likewise take place by their having access to the offal of trichinous pigs, or being actually fed on it. These are, however, exceptions, which, as a matter of course, are of great importance in certain places. As a matter of fact, the rats examined for Trichinella were always found to be severely infected. Thus Billings, in the knackers’ yard at Boston, found that 76 per cent. of the rats were infected, and in an export slaughterhouse 100 per cent. were found to harbour the parasite; in the city of Boston 10 per cent. of the rats had trichinosis. Heller found that of 704 rats, from twenty-nine different places in Saxony, Bavaria, Würtemberg and Austria, 8·3 per cent. were infected with Trichinellæ; of the rats caught in the knackers’ yards, 22·1 were diseased; of those taken in slaughterhouses, 2·3 were infected, and of rats from other localities only 0·3 per cent. harboured the parasite. Leisering found almost the same figures, but in rats from slaughterhouses 5·3 per cent. were infected. The geographical distribution of _T. spiralis_ does not correspond with the occurrence of trichinosis in man; local customs are an important factor; for instance, the custom of eating pork in a condition that does not affect the life of the enclosed trichinella. In places where such customs do not prevail, epidemics do not occur--at the most there are isolated cases of the disease, although there be a great number of infected pigs. The following conditions prevail in North America: In Boston, Billings found that 4 to 5·7 per cent. of the pigs examined were trichinous; Belfield and Atwood found that 8 per cent. were infected in Chicago; Salmon found on an average that 2·7 per cent. were infected (but at various places the percentage fluctuated between 0·28 to 16·3 per cent.), yet epidemics of trichinosis hardly ever occur in North America, and only isolated cases of the disease are met with in German immigrants, who keep to their native customs. This report, according to the researches of H. U. Williams, must be considerably modified. This author has examined the muscular system of human cadavers according to the method employed by inspectors of meat for pigs. The investigations were conducted in the Pathological Institute of the University of Buffalo, and the observer has examined 505 bodies since 1894, of which 27 (= 5·34 per cent.) were invaded by Trichinella. The cases, according to the nationality, are divided as follows:-- ---------------------+----------+--------+---------+------------- | | Trichinella | Percentage | Examined +--------+---------+ of positive | | Absent | Present | results ---------------------+----------+--------+---------+------------- Americans: | | | | (_a_) Whites | 207 | 201 | 6 | 2·89 (_b_) Negroes | 70 | 65 | 5 | 7·14 British and Irish | 62 | 57 | 5 | 8·06 Canadians | 12 | 10 | 2 | 16·66 Germans | 49 | 43 | 6 | 12·24 Italians | 12 | 10 | 2 | 16·66 Other nationalities | 27 | 27 | 0 | 0 Nationality unknown | 66 | 65 | 1 | 1·51 ---------------------+----------+--------+---------+------------- Total | 505 | 478 | 27 | 5·34 ---------------------+----------+--------+---------+------------- It is worthy of remark that half of all the positive cases were mental patients, who were found to be affected with Trichinella to well-nigh 12 per cent. Trichinosis was not, however, the cause of death in any case. Very frequently the Trichinellæ were found calcified and dead. Conditions are similar in most countries of Europe, where, of course, the number of infected pigs is considerably smaller, but the disease depends less on this than on the way in which the pork is prepared. Cases of trichinosis have been known to occur in nearly all the countries of Europe; further, in Egypt, Algeria, East Africa, Syria, India, Australia, and America. North Germany, more especially the Saxe-Thüringian states, is the classical land for epidemics of trichinosis; the mortality varies, but it may be very high.[306] [306] For instance, extensive epidemics occurred in Hettstädt in 1863 (160 patients, 28 deaths); Hanover, 1864–1865 (more than 300 patients); Hadersleben, 1865 (337 patients, 101 deaths); Potsdam, 1866 (164 patients); Greifswald, 1866 (140 cases, 1 death); Magdeburg, 1866 (240 cases, 16 deaths); Halberstadt, 1867 (100 cases, 20 deaths); Stassfurt, 1869 (over 100 cases); Wernigerode, 1873 (100 cases, 1 death); Chemnitz (194 cases, 3 deaths); Linden, 1874 (400 cases, 140 deaths); Niederzwohren, near Cassel, 1877 (half the population); Diedenhofen, 1877 (99 cases, 10 deaths); Leipzig, 1877 (134 cases, 2 deaths); Ernsleben, 1883 (403 cases, 66 deaths); Strenz-Neuendorf, 1884 (86 cases, 12 deaths), etc. According to Johne, 109 epidemics, with 3,402 cases and 79 deaths, occurred in Saxony between 1860 and