CHAPTER III.

THE GERM THEORY OF DISEASE. The Disease-Demon reappears as a Germ.—Phagocytes.—Ptomaines.—Lister’s Antiseptic Surgery.—Sanitary Science or Hygiene.—Bacteriologists.—Faith Cures.—Experimental Physiology and the Latest System of Medicine. Soon after the discovery of the microscope, men began to seek for the causes of diseases in the infinitely little. ATHANASIUS KIRCHER (1598-1680), a Jesuit priest of Fulda, seems to have been gifted with the ability to foresee three of our greatest modern scientific discoveries. He anticipated Darwin’s dictum that life is maintained by struggle and counter-struggle. He described hypnotism in certain animals, and detected, as he thought, micro-organisms with the microscope, then in its infancy, in the blood and pus of patients suffering with the plague and other infectious diseases, which “worms,” as he termed the corpuscles, he considered to be the cause of the disease. His instrument had enabled him to discover that all decomposing substances swarmed with low forms of life. His theory, however, gained little credence at the time.[1043] Next ANTONY VAN LEEUWENHOEK, “the father of microscopy,” in 1675 published his researches in a series of letters to the Royal Society, in which he described minute organisms in waters, vegetable infusions, saliva, and in scrapings from the teeth, and he was able to differentiate these special forms of life. Some of his descriptions are so graphic that microscopists can almost recognise these forms as bacteria with which we are now familiar. Physicians still designating these as “worms” began to attribute to their influence various diseases. In 1701 NICHOLAS ANDRY wrote on this subject a treatise entitled _De la Génération des Vers dans le Corps de l’Homme_. The germ theory of putrefaction and fermentation originated with Andry; he maintained that air, water, vinegar, fermenting wine, old beer, and sour milk contained myriads of germs; he detected these in the blood and pustules of small-pox, and believed that they could be found in other maladies. His views met with general acceptance, and curiously enough it was believed—and has since been verified by our own observation—that mercurial preparations were fatal to such disease germs.[1044] LANCISI in 1718 attributed the unhealthy effects of malarial air to animalcules, and “inconceivable worms” met with as much ridicule in Paris in 1726 as the “microbe” has been received with to-day. Linnæus out of all this chaos thought order might possibly be evolved; he believed that the actual contagion of certain eruptive diseases might be discovered in these small living beings. MARCUS ANTONIUS PLENCIZ in 1762 discussed the relation of animalcules to putrefaction and disease in his works.[1045] Notwithstanding all these clear indications, which, if followed up, would have been fertile in result, the germ theory of disease fell almost into oblivion. OTTO MÜLLER in 1786 began a more systematic study of the life history of various micro-organisms, and thus advanced the science of minute forms of life. The question arose, How do these forms originate? Dr. Needham was the first to suggest the theory of their spontaneous generation. Bonnet, of Geneva, disputed the results of Dr. Needham’s experiments, and Spallanzani demonstrated by experiment the correctness of Bonnet’s criticism. FRANCIS SCHULZE in 1836, by a carefully devised experiment, struck another blow at Needham’s theory of spontaneous generation. In 1837 SCHWANN convinced himself that the cause of decomposition must exist in the air. SCHROEDER and VAN DUSCH in 1854 proved that filtration of the air through cotton-wool was effectual in excluding germs. Then HOFFMAN in 1860, and CHEVREUIL and PASTEUR working independently in 1861, showed that a sterile solution could be kept sterile if the neck of the vessel were bent in the form of an S, so that the micro-organisms in the air entering the neck of the flask, would be deposited by gravitation in the curve. But the advocates of the theory of spontaneous generation were not yet satisfied. They objected that by the boiling of the infusions, etc., under examination they lost the ability to become decomposed; but it was shown that the admission of unfiltered air set up decomposition. PASTEUR, BURDON SANDERSON, and LISTER next showed that blood, urine, and milk would not decompose if proper precautions were taken to avoid contamination. In 1872 CHARLTON BASTIAN endeavoured to rehabilitate the spontaneous generation theory, but TYNDALL effectually disposed of his contentions. It is settled that bacteria, or microbes, as these germs are now called, when once destroyed by heat and by certain chemical agents in any medium, cannot be resuscitated, and that Harvey’s axiom, _omne vivum ex ovo_, applies to all forms of organisms. As DR. SIMS WOODHEAD has said[1046] concerning the battle between the advocates and opponents of the spontaneous generation theory:— “The triumphs of surgery, of preventive inoculation of hygiene in relation to specific infective diseases, of preservation of food, have had their origin in the knowledge gained during the battle which waged round the question of spontaneous generation or _generatio æquivoca_; and to the disciples of that school every acknowledgment must be made and due credit assigned for the attitude of scepticism, and free, ingenious, and honest criticism which they passed concerning half-formed and inadequately-supported theories and imperfectly-conducted experiments, for to their efforts is certainly due the fact that the experiments of their opponents became more and more perfect, and if to-day we have perfect methods of sterilization and of making pure cultivations, it is because nothing was taken for granted, and because able men on both sides of the controversy were ranged against one another to fight the matter to the death.” Another question which had to be determined was whether these organisms were of the animal or vegetable kingdom. EHRENBERG came to the conclusion that in consequence of snake-like and rotary movements of certain micro-organisms they were animals; and this opinion held its ground till DAVAINE decided that bacteria must be considered as belonging to the vegetable kingdom. Up to 1852 the animal theory was unshaken; in 1854 COHN demonstrated the plant nature of bacteria. In 1857 NAEGELI made a group of all the forms of lesser minute organisms, and termed it Schizomycetes, or fission fungi. The connection between micro-organisms and disease was the subject of research also in another direction. The discovery by LATUM and SCHWANN in 1837, that the yeast plant is a living organism, and the true cause of fermentation, threw great light on the whole inquiry. Many observers had long recognised the likeness of certain diseases to fermentation processes, and it gradually became the opinion that such diseases were similarly produced. In 1837 BASSI discovered that the silk-worm disease was due to microscopic spores on the bodies of sick worms, and that healthy worms became diseased when these spores were conveyed to them. HENLE in 1840 declared that all contagious diseases must be caused by the growth of something of a living nature, although he had searched in vain for the living contagion of small-pox and scarlet fever. When fungi were found to be the cause of favus, herpes tonsurans, and pityriasis versicolor, the theory received a still greater impetus. SWAINE, BRITTAN, and BUDD found micro-organisms in connection with cholera. In 1857 PASTEUR demonstrated that lactic, acetic, and butyric fermentations were produced by micro-organisms.[1047] In 1863 DAVAINE came to the conclusion that the disease known as splenic fever is caused by an organised being which kills the animal by multiplying in its blood, and so changing its nature, after the manner of a fermentation process. PASTEUR next took up the investigation of silk-worm disease, and was ultimately able to confirm the opinion that the disease was due to micro-organisms, and to devise a remedy for it. ROBERT KOCH in 1877 described the life-history of the bacillus of anthrax or splenic fever. PASTEUR also devoted much attention to the same subject, and confirmed the observations of Koch. PAUL BERT, on the other hand, argued that the bacilli were of no importance. Ultimately he was convinced of his error by Pasteur; it was, however, says PROFESSOR CRUIKSHANK,[1048] “principally the researches of Koch which placed the doctrine of contagium vivum on a scientific basis. Koch elevated the theory of contagium vivum to a demonstrated and established fact.” The whole matter is beset with fallacies. Because certain bacteria have been discovered in the blood of animals suffering from a particular disease, it must not be rashly concluded that these bacteria are always its cause, they may be in some cases only its effects. At the present time the nature of the contagion in many diseases, such as hydrophobia, variola, vaccinia, scarlet fever, and measles, has not been discovered. The comma-bacillus is associated with cholera in some mysterious manner, yet experimenters have swallowed myriads of comma-bacilli, and have remained never the worse. Although Pasteur’s prophylactic treatment against hydrophobia is based upon the theory that a micro-organism is the cause of the disease, Pasteur has never yet discovered the bacterium of hydrophobia, yet there would seem to be one. DR. SIMS WOODHEAD says:[1049] “It is a most remarkable fact that although no micro-organisms can be found in the virus, filtration through the Pasteur filter keeps back the effective part of the virus, whilst heating to 100°C. destroys the activity of the virus.” The disease-demon has now reappeared in the form of a germ. THE PHAGOCYTE THEORY. Some thirty-six diseases, many of which are amongst the most terrible which afflict men and animals, are attributed by bacteriologists to micro-organisms.[1050] It is sufficiently alarming to reflect that enemies which can only be detected by a specialist armed with a powerful microscope are everywhere around us, waiting to attack us in a favourable spot, and slay us without hope of escape. Yet the germ-theorists have not left us entirely without hope. One of Pasteur’s most distinguished pupils, M. METSCHNIKOFF, offers us salvation through faith in his phagocytes. The white blood corpuscles are for ever on the watch for the incursions of disease germs. These they instantly arrest and imprison by taking them into their own substance, digesting and converting them to their own uses. Whenever there is an extra demand for the services of these admirable blood-police, a large number are attracted to the point where the burglarious and murderous enemy has entrenched himself; and if the system is in a position to maintain a sufficient force of these guardians of health, the enemy is rapidly digested, and the effete products are expelled by the regular physiological channels. It has been found that men and animals may be insusceptible to an infective disease by natural immunity. Not all persons subjected to exposure to epidemic diseases contract them. Ordinary sheep readily succumb to anthrax, but Algerian sheep resist any but large doses of the virus.[1051] Acquired immunity is that by which one attack, say of measles or of small-pox, protects against a second. Acclimatization also affords immunity. Pasteur, in his researches on fowl cholera, noticed that in non-fatal cases the disease did not recur. This set him to work out a theory of attenuated inoculations which should afford protection by giving the disease in a mild form in cultivations of the micro-organism. Pasteur next endeavoured to protect animals against anthrax by inoculating them with a mitigated virus. His results were criticised and his researches opposed by Koch, who came to the conclusion that the process did not admit of practical application, chiefly because the immunity would only last a year, and on account of the danger of disseminating a vaccine of the necessary strength.[1052] The theory of protective inoculation in hydrophobia has been much discussed. Pasteur’s explanation does not entirely satisfy some experts. Dr. Sims Woodhead gives the following: “I am inclined to think that the explanation advanced by Wood and myself, that the treatment consists essentially in causing the tissues to acquire a tolerance before the microbe has had time to develop, is more in accordance with the facts. The tissue cells are acted upon by increasingly active virus, each step of which acclimatizes the cells for the next stronger virus, until at length, when the virus formed by the micro-organisms introduced at the time of the bite comes to exert its action, the tissues have been so far altered or acclimatized that they can continue their work undisturbed in its presence; and treating the micro-organisms themselves as foreign bodies, destroy them. When the cells are _suddenly_ attacked by a _strong dose_ of the poison of this virus, they are so paralysed that the micro-organisms can continue to carry on their poison-manufacturing process without let or hindrance; but when the cells are gradually, though rapidly, accustomed to the presence of the poison by the exhibition of constantly increasing doses, they can carry on their scavenging work even in its presence, and the micro-organisms are destroyed, possibly even before they can exert their full poison-manufacturing powers.”[1053] PTOMAINES. The germ theory has thrown great light upon the subject of certain mysterious organic poisoning processes, which long puzzled analysts and physicians. Diseased meat, fish, cheese, and other articles of food frequently cause symptoms of poisoning in those who have partaken of them. The analyst failed to detect the precise agent which caused the mischief, and it was not till the bacteriologists investigated the subject that it was satisfactorily explained. In 1814, BURROWS described a poisonous substance in decaying fish. In 1820, KERNER described a poisonous alkaloid which he discovered in sausages. In 1856, PANUM isolated a poison from some decomposing animal matter. ZUELZA and SONNENSCHEIN from the same substance obtained a poison which closely resembled atropine in its physiological action. SELMI between 1871 and 1880 described substances which he called cadaveric alkaloids or ptomaines. Pasteur and others, working in the same direction, have greatly advanced our knowledge of these deadly agents. Bacteria are now known to have the power to build up deadly substances as they grow in dead or living animal tissues, just as plants build up poisons in their own tissues; these substances exert a deadly influence on the nerve centres, and hence a cheese bacillus may be as dangerous to human life as a dose of aconite. LISTER’S ANTISEPTIC SURGERY. What is commonly known as “Listerism” is a development of the germ theory of disease, which has revolutionised the art of surgery by its direct and indirect influence. Pus formation, the result of destructive processes which prevent the healing of wounds, was discovered to be due to the action of germs falling from the atmosphere on the injured flesh. LISTER sought to destroy these germs by powerful disinfectants. This was the first step in the antiseptic treatment. When carbolic-acid lotions were applied for this purpose, LISTER discovered that the wound healed rapidly. He believed that he had destroyed the micro-organisms by the carbolic-acid lotions. But LISTER improved on this process, and seeing how difficult it is to destroy the germs when they have once entered the tissues, he invented a method whereby they were prevented from gaining admission at all. He fought the micro-organisms in the atmosphere of the operating room, in the dressings, instruments, and hands of the operator, and thus gradually built up his system of absolute surgical cleanliness called antiseptic surgery. Even those surgeons who rejected his method in its entirety, and declined to adopt his complicated system of dressings, devoted so much attention to the minutest cleanliness, that they achieved results not less successful than those of the inventor of the antiseptic system itself. SANITARY SCIENCE. Hygiene, the art of preserving health, has always been recognised as a branch of medical science, not less important than that which concerns itself with the cure of disease. MOSES (B.C. 1490) enjoined the strictest cleanliness, and anticipated our modern sanitary laws. HIPPOCRATES embodied in his works treatises on hygiene, which existed in Greece probably long anterior to his time. The value of attention to rules of diet and exercise was recognised by HERODICUS, one of his preceptors, who introduced a system of medicinal gymnastics for the improvement of the health and the cure of disease. Such rules must to a greater or less extent have always been in force in any well-constituted army. Gymnasts, athletes, and others must have been fully aware of the necessity for attending to such rules. Hippocrates, in his treatise _Airs, Waters, and Places_, has insisted on the duty of the physician to study the effects of the seasons, the winds, the position of cities, and the diseases which are endemic and epidemic in them, the qualities of waters, and their effects on public health, and so forth. Had men taken up the study of Hygiene where Hippocrates left off, we should not have heard of the plagues, pestilences, and epidemics which up to modern times periodically devastated the civilized world. HYGIENE. Mr. PARKES, in the introduction to his _Manual of Practical Hygiene_, defines hygiene in its largest sense to signify “rules for perfect culture of mind and body.” The two are not to be dissociated. Every mental and moral action influences the body; the physical conditions equally re-act upon the mind. He admirably says: “For a perfect system of hygiene we must combine the knowledge of the physician, the schoolmaster, and the priest, and must train the body, the intellect, and the moral soul in a perfect and balanced order. Then, if our knowledge were exact, and our means of application adequate, we should see the human being in his perfect beauty, as Providence, perhaps, intended him to be; in the harmonious proportion and complete balance of all parts in which he came out of his Maker’s hands, in whose divine image, we are told, he was in the beginning made.” Mr. Parkes asks if such a system is possible? He replies that we can even now literally choose between health and disease. There are certain hereditary conditions which we may not be able to avoid, and men may hinder our acquisition of the boon; but as a race man holds his own destiny in his hands, and can choose the good and reject the evil. Exit the disease-demon! Fevers and other epidemic diseases are no longer attributed to the anger of the Supreme Being; they may be prevented. If we use the words scourge, plague, visitation, and the like, it is merely because we recognise that Nature can take offence at our violation of her laws, and visit us with the penalty. One of the most important events of our time was the establishment of the Registrar-General’s office in 1838. To DR. WILLIAM FARR we owe a nation’s gratitude for the admirable manner in which he performed the duties of his office. The Government Inquiry into the Health of Towns and of the Country generally, undertaken by EDWIN CHADWICK, SOUTHWOOD SMITH, NEIL ARNOTT, SUTHERLAND, GUY, TOYNBEE, and others, was of immense importance to the national health. The medical officer to the Privy Council, SIMON, carried on the work thus ably commenced with the greatest vigour; and the consequence of the important departure was that medical officers of health were appointed to the different towns and parishes. Various public health acts have followed from time to time, and it has been found, in the words of Mr. Parkes, that “nothing is so costly in all ways as disease, and that nothing is so remunerative as the outlay which augments health, and in doing so, augments the amount and value of the work done.” It is a reproach frequently brought against medicine that it makes little advance. Some have even said that in some respects we are no better off than if we lived in the days of Hippocrates. However this may be, we may be justly proud of the splendid work which hygienic medicine has performed, and we have every reason to look hopefully forward to the benefits this branch of medical science will confer upon us in the near future. Hygiene is the outcome of physiology. Until we knew the laws of life, it was impossible that hygiene should have a scientific basis; and henceforth physiology and hygiene will go hand in hand.[1054] JOHN SIMON, C.B., F.R.S. (born 1816), the eminent physiologist, pathologist, and surgeon, became the first appointed officer of health to the City of London. He was for some time medical adviser to the Privy Council. He rendered the greatest services to the health of the nation by his reports and official papers on sanitary matters. EDMUND A. PARKES (1819-1876) was the great sanitary reformer whose name is gratefully enshrined in the “Parkes Museum of Hygiene,” instituted in 1876, of University College, London. LUDWIG J. P. SEMMELWEIS (1818-1865), “the Father of Antiseptic Midwifery,” was professor in Pesth, and has earned the gratitude of his profession and of the whole world by demonstrating that puerperal fever was due to inoculation, that the poison which caused it was introduced by organic matter below the nails and epidermis of the students and doctors who had been engaged in anatomical or pathological work and had not taken sufficient pains to disinfect and purify their hands. He recommended careful washing with chlorine water before each examination; the consequence of which was, that the mortality among lying-in women fell in two months from twelve to three per cent. He anticipated the methods of Lister, and died in a lunatic asylum, galled by the attacks which his doctrines experienced.[1055] Sir Andrew Clark said:[1056] “There are few such parallels in the history of science, in regard to his tremendous moral heroism; in spite of every conceivable difficulty, in positions of misrepresentation, in spite of persecution, he continued his labours, until crowned with a full clearing up of the difficulties. As to his martyrdom, there is not such a history. The persecution to which he was exposed in the later years of his stay in Vienna, his being hounded out of Vienna and settling in Budapest, and his premature end in loss of reason, form indeed a sad story, and one of the highest examples that can be presented.” BACTERIOLOGISTS AND OTHER SCIENTISTS. BENJAMIN W. RICHARDSON, M.D., F.R.S., etc. (born 1828). In 1865 he made important researches on the nature of the poisons of contagious diseases and discovered _septine_. In 1866 he discovered the use of the ether spray for locally abolishing pain in surgical operations. He introduced bichloride of methylene as an anæsthetic, and discovered the influence of nitrite of amyl over tetanus, angina pectoris, etc. He invented the _lethal chamber_ for killing animals without pain, and has made many most important researches on the action of alcohol on man. In 1875 he gave a sketch of a “Model City of Health,” to be called Hygeia, which awakened much interest and discussion. JOHN BURDON SANDERSON, M.D. (born 1828), Professor of Physiology at Oxford, made investigations respecting the cattle plague, 1865-66. In 1883 he sat on the Royal Commission on Hospitals for infectious diseases, and has made elaborate researches on animal and plant electricity, and on the nature of contagion. ROBERT KOCH (born 1843), the eminent bacteriologist, the discoverer of the “comma” bacillus, and the tubercle bacillus, is Professor of the Institute of Hygiene in Berlin. JOHN TYNDALL, F.R.S. (born 1820), is one of the foremost of the scientific explorers of the century. Besides his researches in relation to magnetism, radiant heat, heat as a mode of motion, light, etc., Professor Tyndall has rendered very important services to medicine by his studies on _The Floating Matter of the Air in Relation to Putrification and Infection_, 1881. LOUIS PASTEUR (born 1822), chemist, is celebrated for his researches relative to the polarization of light, and for his investigations on fermentation, the preservation of wines, and the propagation of zymotic diseases in silkworms and domestic animals. Pasteur’s most important work for medicine was the demonstration of the existence of the germs which cause putrefaction. The Minister of Public Instruction, addressing M. Pasteur on the occasion of his seventieth birthday, summed up what is known as Pasteurism in the following words: “Henceforward the formula is definitive and complete. Your disciples give it in two words—ferments and virus are living beings; vaccine is an attenuated virus, the basis of medicine is the artificial attenuation of virus, and thus the microbic treatment is founded.” Pasteur’s later work has been chiefly in connection with the attempt to discover a prophylactic for hydrophobia. LIONEL S. BEALE, F.R.S. (born 1828), physiologist and pathological anatomist, is a celebrated microscopist, author of _The Microscope in its Application to Practical Medicine_; _Disease Germs, their Supposed and Real Nature, and on the Treatment of Diseases caused by their Presence_; and many other works of equal importance to medical science. WILLIAM B. CARPENTER (1812-1885) was a celebrated physiologist, whose great work has done more to popularise the study of physiology amongst non-professional, as well as medical readers, than any other, except that of Professor Huxley, which followed it. Amongst other scientific workers of the century may be mentioned PURKINJE, who rediscovered and described the bone corpuscles, contributed greatly to the study of microscopical anatomy and ophthalmology by his experiments with the ophthalmoscope. R. WAGNER (1805-1864) in 1861 called an anthropological congress, which was attended by several distinguished anatomists, and thus originated the “Anthropological Congress.” PANDER (1794-1865) and BAER (1792-1876) made important researches in the history of development. To Baer is due the splendid discovery of the mammalian ovum. FRANÇOIS MAGENDIE (1782-1855) was the first to introduce the experimental method into pathology and pharmacology. His investigations in what are called pharmaco-dynamics, chiefly connected with the alkaloids, introduced many of these powerful remedies into medical practice. He admitted a vital principle in nervous activity, but for the rest endeavoured to reduce medicine to mere physiological and chemical laws. MIRACLES OF HEALING, FAITH CURES, MIND CURES, CHRISTIAN SCIENCE HEALING, ETC., ETC. There are many things connected with the healing art on which the public mind is better informed than the recognised authorities on medicine. Mesmerism is now accepted by the faculty under the name of hypnotism, and the miracles of healing wrought at the shrines of saints, long the objects of scorn and contempt at the hands of the medical profession, are now declared to be well within the domain of scientific fact. The miracles of Lourdes, the faith cures at Bethshan, and similar phenomena, having been subjected to the strictest investigation by the most competent medical authorities, are proved to be not impostures and delusions, but simple matters of fact. Science having reluctantly accepted the faith-cure, now declares it to be “an ideal method, since it often attains its end when all other means have failed.”[1057] Professor Charcot, while declaring that the faith-cure is entirely of a scientific order, insists that its domain is limited; “to produce its effects it must be applied to those cases which demand for their cure no intervention beyond the power which the mind has over the body.” That is to say, faith will cure paralysis and other disorders of motion and sensation dependent on idea, but does not avail to restore a lost organ or an amputated limb. Professor Charcot believes also that the faith-cure may cause ulcers and tumours to disappear, if such lesions be of the same nature as the paralysis cured by the same means. In all this there is no miracle. The diseases are all of hysterical origin, according to this eminent authority, and being purely dynamic, and not organic, the mind has power to influence and cure them. The mind of the invalid becomes possessed of the overpowering idea that a cure is to be effected, and it is so. M. Littré has explained for us how this happens.[1058] The mind, which is most eminently receptive of suggestion, will be the most likely to be influential in curing the body in which it is enshrined, by the powerful force of auto-suggestion.[1059] In expressing this opinion, no question need arise of the efficacy of prayer or of the intervention of the Divine power. The aim of the physician is to understand the medical side of the subject, and science is daily becoming more capable of offering an explanation of such phenomena from a purely medical point of view. A curious instance of faith-cure was recently given in a Catholic magazine. The _Month_ for June, 1892, published an account, by the late Earl of Denbigh, of a cure worked by a member of a family named Cancelli on Lady Denbigh in 1850. She was suffering severely from rheumatism, and the Pope (Pius IX.) mentioned to the Earl that near Foligno there was a family of peasants who were credited with a miraculous power of curing rheumatic disorders. Lord Denbigh succeeded in getting one of the family, an old man, to come, and learned from him the legend of the cure. The belief was that in the reign of Nero, the Apostles Peter and Paul took refuge in the hut of an old couple named Cancelli, near Foligno, and as a proof of gratitude, gave to the male descendants of the family living near the spot the power of curing rheumatic disorders to the end of time. Lord Denbigh described how the old man made a solemn invocation, using the sign of the cross, and, in fact, Lady Denbigh did recover at once. In a few days the pains returned, but she made an act of resignation, and they then left her, and never returned with any acuteness. EXPERIMENTAL PHYSIOLOGY. The question of vivisection, or experimental physiology, pathology, and pharmacology, has become a burning one in England and America of recent years. In a history of medicine so prominent a question cannot be entirely ignored, although it would be out of place to discuss it here at length. It has been claimed that almost all our real knowledge of the healing art, and the most important steps of medical progress, have been gained by experiments upon living animals. On the other hand, it has been maintained by practical physicians and surgeons that the method in question is not less misleading than cruel; that “the only correct path is that of thoughtful experience.”[1060] On behalf of the advocates of the experimental method, PROFESSOR MICHAEL FOSTER shall state the case; that of the other side shall be given in the words of SIR ANDREW CLARK, “the prince of physicians, and one of the noblest of men,” under whom it was my happiness and privilege to study medicine in the wards of the London Hospital. PROFESSOR MICHAEL FOSTER says: “It would not be a hard task to give chapter and verse for the assertion that the experimental method has, especially in these later times, supplied the chief means of progress in physiology; but it would be a long task, and we may content ourselves with calling attention to what is in many respects a typical case. We referred a short time back to the phenomena of ‘inhibition.’ It is not too much to say that the discovery of the inhibitory function of certain nerves marks one of the most important steps in the progress of physiology during the past half-century. The mere attainment of the fact that the stimulation of a nerve might stop action instead of inducing action constituted in itself almost a revolution; and the value of that fact in helping us on the one hand to unravel the tangled puzzles of physiological action and reaction, and on the other hand to push our inquiries into the still more difficult problems of molecular changes, has proved immense. One cannot at the present time take up a physiological memoir covering any large extent of ground without finding some use made of inhibitory processes for the purpose of explaining physiological phenomena. Now, however skilfully we may read older statements between the lines, no scientific—that is, no exact—knowledge of inhibition was possessed by any physiologist, until Weber, by a direct experiment on a living animal, discovered the inhibitory influence of the pneumogastric nerve over the beating of the heart. It was, of course, previously known that under certain circumstances the beating of the heart might be stopped; but all ideas as to how the stoppage was, or might be, brought about, were vague and uncertain before Weber made his experiment. That experiment gave the clue to an exact knowledge, and it is difficult, if not impossible, to see how the clue could have been gained otherwise than by experiment; other experiments have enabled us to follow up the clue, so that it may with justice be said that all that part of the recent progress of physiology which is due to the introduction of a knowledge of inhibitory processes is the direct result of the experimental method. But the story of our knowledge of inhibition is only one of the innumerable instances of the value of this method. In almost every department of physiology, an experiment, or a series of experiments, has proved a turning-point at which vague, nebulous fancies were exchanged for clear, decided knowledge, or a starting-point for the