CHAPTER V.

OF THE PRIVILEGES AND DUTIES OF PHYSICIANS AND SURGEONS WHEN SUMMONED AS EXPERT WITNESSES IN COURTS OF JUSTICE.[180] _Introductory—Distinction Between Expert Witnesses and Other Witnesses._—One of the most important positions that a medical man is called upon to assume by virtue of his professional character, is the position of expert witness. Most writers on medical jurisprudence confine themselves, in the discussion of this subject, to presenting the medico-legal rules which appertain to this position, and concede its high importance. Before defining what is meant by the term expert witness, or treating of the rules which determine the status of such witnesses in court, and their duties, it seems advisable to introduce the subject by a brief consideration of the distinction between ordinary witnesses and expert witnesses. When medicine and law are united in the purpose of investigating facts, and bringing about a legal determination as to what are or are not facts, they co-operate with each other in this way. The law furnishes the machinery for the inquiry and the rules which determine how it shall be prosecuted. The medical man, however, is called upon as an assistant to the law, because of his skill and experience in his profession, which enable him to ascertain and interpret the circumstances from which the facts sought to be established are to be inferred. Ordinary witnesses testify concerning matters of observation, the court and jury being endowed with the sole power to determine the credibility of their evidence and the true result of their observations. Yet the border line of distinction between witnesses who testify merely to actual matters of observation, and those who give their opinions upon and draw inferences from established facts and circumstances, is a wavering one. The general rule of evidence is well understood, that hearsay evidence is inadmissible, and yet, like any other rule, this has its exceptions which grow out of the necessities of given cases. This is so because there are and always will be, matters brought before courts for investigation and determination, long after the witnesses who personally saw the facts and circumstances of the particular case in which such matters are concerned have died, or have withdrawn beyond the reach of the process of the court. Possibly no record in writing of such facts and circumstances has been left, or if in writing it lacks the sanctity of being a judicial writing, and hence is no better evidence than any other form of hearsay evidence. For this reason in matters of family history, pedigree, custom, and the like, hearsay evidence is permitted, and is entitled to as much weight as any other evidence, if the witnesses giving it be trustworthy. _In Matters of Common Experience Witnesses in General Often State Conclusions._—Moreover, in matters of common experience, the testimony of any witness, if carefully analyzed, often shows that he is sometimes allowed to draw, and state, his conclusions and inferences, instead of being required to confine his evidence simply to telling in the strictest possible way, and with the closest limitations, what he actually witnessed. A good illustration of this is the case of a person who sees a crime of homicide committed by shooting, and is called upon to testify in court. He would be allowed to testify that the defendant, if he could identify the prisoner at the bar as such, was the person whom he saw fire the shot, although he might not have examined him with close scrutiny, and might never have seen him before the crime. In saying that the defendant was the person who fired the shot, while he would be in terms testifying to a fact, he would still be drawing an inference, and giving an opinion, based upon his recollection of the person whom he saw engaged in the act of firing, and of the likeness or resemblance of such person to the prisoner at the bar, which would be a matter of comparison and of opinion. So, too, although he could not see the bullet take its course from the mouth of the gun and imbed itself in the body of the deceased, yet if he saw the firing, heard the explosion, saw the flash and smoke of the powder, observed the direction in which the accused pointed the weapon, and saw the deceased stagger and fall, he would be allowed to testify in answer to a direct question whether or not the accused shot the deceased. And, yet in making up that answer he would be testifying not simply to a matter of actual observation, but to a conclusion. As it is in reference to the question of identity so it is as to many other matters which come before our courts, in all of which the witnesses are permitted, without objection, to testify to conclusions and to give answers which are the result of inferences which they draw themselves, rather than a statement of their actual observations. The law is not a metaphysical but a practical science, limited and confined by the practical restrictions which experience has shown must be put upon it, in order to enable it to accomplish its object of administering justice between man and man. Men form such conclusions as have been indicated, instinctively and unconsciously, and it would be practicably impossible for them to narrate any occurrence without embodying in their narration some of these natural and unconscious conclusions. The law, therefore, includes among the matters which witnesses are permitted to characterize as facts, those daily and hourly inferences and deductions which all men are accustomed to make, and concerning which no two men who are properly constituted can greatly differ. It is true that this practice sometimes leads to error, but it has grown out of necessity. The greatest safeguard is, that upon the trial of a question of fact both sides are represented by counsel, and the opportunity which cross-examination offers to an advocate of even reasonable and ordinary skill is such, that these conclusions and inferences may be sifted down through the chain of observation, and the process of drawing these conclusions and inferences from a series of facts, tested in such a manner that the improbability, probability, or truth of any given inference or conclusion may be determined with substantial accuracy. The illustrations which have been given above exhibit the simplest form in which so-called direct testimony can be demonstrated to be not always positive and direct testimony, but somewhat a matter of inference. Other examples and illustrations of common occurrence will exhibit still more closely the line between actuality and opinion. At times it becomes essential to the determination of a question, that the courts should know whether or not a person was angry, whether or not he was intoxicated, or whether or not at a given time, when his mental status was under observation, he acted rationally or irrationally. Lay witnesses have for many years been permitted to testify from observation, and without possessing any special qualification to do so, as to the existence or non-existence of such conditions as those just mentioned in a person whose actions are under consideration. It is manifest that in making any such inferences the witnesses’ testimony is mainly a conclusion based on inference. Take the case of anger. How shall that be determined? It is difficult to describe anger. A loud voice, a flushed face, the use of bitter words, nervous, excitable, demonstrative action—all these symptoms might occur, or but few of them might occur. So, too, in the matter of intoxication. It is well known that some individuals exhibit the effects of intoxicants in an entirely different manner and degree from others. Some men who are very much intoxicated, so as to be quite incapable, in the eye of the law, of forming a criminal intent, or of contracting an obligation which would be valid, may still be able to walk perfectly straight, or to talk without much confusion. Others, whose walk and demeanor would indicate a considerable degree of intoxication, might be mentally clear and unruffled and even stimulated by intoxicants to precise mental co-ordination and reasoning. Again, there are persons, as to whom a witness, after stating that he had observed them, and after stating the particular matters and things in which such persons were engaged, might with apparent accuracy state that they acted rationally or irrationally, and yet such persons might nevertheless, upon further examination, be found to have been acting according to a particular custom or habit, or idiosyncrasy of long years’ standing. Thus it is apparent that in each of these cases, when the witness attempts to state what, out of necessity, the court treats as a fact—viz., whether a given person is or is not angry, or intoxicated, or irrational—the witness is really testifying to the result, in his own mind, of his observations of the condition and conduct of the person who is under investigation, when compared with a standard which the witness has erected for himself. Hence such results are really matters of opinion evidence, pure and simple. Other examples of a like character are found in statements as to weight, height, distance, speed, and the like, as to which men of common powers of observation, who are not strictly experts, are, because of convenience and necessity and the probability of reasonable and ordinary accuracy, commonly permitted to give their own judgment and conclusions as evidence. _All Witnesses Often Permitted to Draw and State Conclusions in Matters involving Numerous and Complicated Details._—Thus the practical necessity of the administration of justice has led to the establishment of the rule, that where the details of an occurrence are numerous and complicated, and are incapable of precise description by ordinary observers, witnesses are permitted to use, in testifying, general expressions which really embody their conclusions from the facts or details observed by them. Greenleaf on Evidence, Section 440, note A; Wharton on Evidence, Section 434. Wharton says that “the distinction between expert witnesses and ordinary witnesses is this: the non-expert witness testifies to conclusions which may be verified by the adjudicating tribunal; the expert, to conclusions which cannot be so verified. The non-expert gives the results of a process of reasoning familiar to every-day life; the expert gives the results of a process of reasoning which can be determined only by special scientists.” See also People _v._ Fernandez, 35 N.Y., 49. People _v._ Deacons, 109 N.Y., 374-382. This learned writer (Wharton) also says, at Section 437 of the same treatise: “Where conclusions depend upon facts whose evidential weight can only be determined by those familiar with a particular specialty, then these conclusions may be given by experts in such specialty.” Such also is the exact derivative meaning of the word expert, it being derived from the Latin word “_expertus_,” meaning, literally, “experienced,” and hence skilled by experience. _Functions of an Expert Witness Essentially Judicial._—It is the function of an expert witness to reason about facts, to explain their connection with one another, and to draw conclusions and inferences from them. Hence, a witness, however expert in any ordinary sense in his specialty, when he is called upon merely to narrate facts which he has observed, is an ordinary witness, and is governed by the same rules which apply to the ordinary witnesses. When, however, he is called upon, in addition to recounting facts, to explain or interpret them by reference to assumed facts, he becomes properly an expert witness. It thus appears that an expert witness must necessarily perform a part of the duties which devolve upon the court or the jury. His position is, therefore, essentially judicial, except that he has no power to enforce his determinations by judicial process. The importance and responsibility which the law thus confers upon an expert are of the highest character. He ranks the coequal with the tribunal itself in his peculiar province, so far as relates to his individual responsibility. That this should tend to elevate such witnesses to a high social position, and ought to require the most exact and faithful integrity of purpose and statement, is self-evident. _Difference Between Status of Expert Witnesses in France and Germany and in the United States and England._—In some foreign countries, notably in Germany and in France, experts in medico-legal matters have an assured official position, and are generally not allowed to be selected at hap-hazard according to the will or the length of the purse of those who need their services. The consequence of this method of obtaining expert evidence is, that expert witnesses in those countries command a high measure of respect and honor. Unfortunately, however, in this country, where the opposite practice prevails, the weaknesses of human nature are such that the common people, newspapers, lawyers, and even the courts in some recorded opinions and decisions, have come to express a great want of confidence in the weight and value of expert testimony. This deplorable result of a bad system of procedure is universally recognized, yet our State legislatures have as yet refrained from attempting to correct it. Hence, in considering the value of expert testimony _in matters of medical jurisprudence_, it must be conceded, in the first instance, that the difference between the system prevailing in this country and in England, and that which prevails on the Continent, notably in Germany and France, has not tended to raise but to depress the value of such testimony in the first-named countries. In the latter countries, the experts upon medico-legal questions are officers of the court, or are treated as such. They form, in a sense, a part of the judicial system, and the expression of their opinions consequently carries with it great weight. Moreover, under the system which prevails there, it has been possible for men to be educated up to a high degree of skill and experience in the particular branches of physiological or psychological or physical investigations which they pursue, while here in America, and to a certain extent also in England, experts are such for other reasons, and by the operations of other causes, than the fact of their permanent employment in that capacity. As a general thing they become skilled in their profession or in the particular branches of it in which they practise as specialists, and are summoned to testify simply because they are selected by one party or another to a lawsuit. _Mr. Wharton’s View of this Question in the Main Hostile to the Prevailing System Here._—The effect of the methods which thus prevail has not been entirely to the advantage of the medical profession or of our courts. Wharton, in his work on “Evidence,” Section 454, observes upon this point: “When expert testimony was first introduced it was regarded with great respect. An expert was viewed as the representative of a science of which he was a professor, giving impartially its conclusions. Two conditions have combined to produce a material change in this relation. In the first place it has been discovered that no expert, no matter how learned and incorrupt, speaks for his science as a whole. Few specialties are so small as not to be torn by factions, and often the smaller the specialty the bitterer and more inflaming and distorting are the animosities by which these factions are possessed. Particularly is this the case in matters psychological, in which there is no hypothesis so monstrous that an expert cannot be found to swear to it on the stand, and to defend it with vehemence. ‘_Nihil tam absurdo_,’ which being literally translated means that there is nothing so absurd that the philosophers won’t say it! In the second place, the retaining of experts by a fee proportioned to the importance of their testimony is now as customary as is the retaining of lawyers. No court would take as testimony the sworn statement of the law given by counsel retained on a particular side, for the reason that the most high-minded men are so swayed by an employment of this kind as to lose the power of impartial judgment; and so intense is this conviction that in every civilized community the retention by a judge of presents from suitors visits him not only with disqualification but disgrace. Hence it is that, apart from the partisan character of their opinions, their utterances, now that they have as a class become the retained agents of the parties, have lost all judicial authority and are entitled only to the weight which sound and consistent criticism will award to the testimony itself. In making this criticism a large allowance must be made for the bias necessarily belonging to men retained to advocate a cause, who speak not as to fact but as to opinion, and who are selected, on all moot questions, either from their prior advocacy of them or from their readiness to adopt the opinion to be proved. In this sense we may adopt the strong language of Lord Kenyon, that skilled witnesses come with such a bias on their minds to support the cause in which they are embarked, that hardly any weight should be given to their evidence.” This author then proceeds to show that under the civil law system the conclusions of experts were formerly treated as unassailable facts, but under the English and American common law system this is not the case, but their testimony is to be weighed by the court. He says: “The grounds on which the conclusion is reached may be asked for: the expert’s capacity for drawing conclusions, as well as his premises, may be assailed. Cases of conflict are to be determined, not by the number of witnesses, but by the weight of their testimony, and though the opinion of an expert of high character may be entitled to great respect, yet if questioned, its authority must ultimately rest upon the truth, material and formal, of the reasoning on which it depends.” Judge Davis, of the Supreme Court of Maine, in Neil’s case (cited in Wharton and Stille’s “Medical Jurisprudence,” Vol. I., Section 294), said: “If there is any kind of testimony that is not only of no value, but even worse than that, it is in my judgment that of medical experts. They may be able to state the diagnosis of a disease more learnedly, but upon the question whether it had at a given time reached a stage that the subject of it was incapable of making a contract, or irresponsible for his acts, the opinions of his neighbors, of men of good common sense, would be worth more than that of all the experts in the country.” Such stinging criticisms as these, and others which might be cited, of a like character, may not be always merited. It is certain that medical experts’ opinions, if fully enlightened by scientific research and free from partisan bias, ought to occupy a position like that of judicial opinions in weight and decisiveness upon the questions submitted to them. Such was the position occupied in the public estimation, and in that of judges and counsel, by the great Dr. Caspar in Germany, and Foedere or Pinel, and others since their time, in France. But this position was acquired chiefly because of the fact already mentioned, that under the system of administration of justice which prevails in those countries these great men were regarded, and acted, as a component part of the judicial system. They were called in as officers of the law to assist the court in forming a judgment, and determining disputed questions of fact, in cases involving life and death, or the devolution of property, where scientific experience, knowledge and skill, not possessed by judges or by counsel, was necessary for the determination of the questions involved. The root of the evil in America is, as already pointed out, to be found in the system which allows parties to retain and pay their own experts without any substantial restrictions. Sooner or later, among the other reforms in our judicial system, it will be found necessary to reform this evil by the enactment of laws requiring that the witnesses in medico-legal cases, particularly those in which a crime is alleged to have been committed, shall be designated by the court, or by some public authority, and paid from the public treasury instead of by the parties. Such experts would then occupy their proper position of special counsel, advising and assisting the legal counsel and the court, but they would not be taken out of this sphere and put in the utterly inconsistent one of witnesses. Their status and their duties would be as clearly distinguished from that of expert witnesses as now known, as the status and duty of the lawyer are from the status and duty of the judge. The present system has been said to be very much like putting a lawyer, who has just argued his client’s case, on the bench to decide it. Whether experts should be appointed as permanent government officials, like our judges, or should be selected specially for each case like juries, referees, or arbitrators, and in the latter event whether they should be nominated by the parties and selected by the court from such nominees, or otherwise, are all questions of detail. Our judges and lawyers seem slow to recognize the fact that the duties of experts are judicial, or at least quasi-judicial; to pass upon certain facts which neither the court nor the jury can understand without their aid. But, as we have seen from the citations just given, judges and lawyers have fully recognized the unreliability of expert testimony, produced as it now is in England and in this country at the whim and selection of the parties and paid for, much or little, according to the means of the parties.[181] _Method of Preliminary Examination of Experts—On Medical Questions a Licensed Physician Presumed Competent._—As the system exists here, the only power that the court has over the selection of an expert, is to determine, in advance of his testimony and of the elucidation of his opinions, whether or not he is competent as an expert. But this power affords little or no check or restriction, because in the effort to get all the light that is possible upon the questions under consideration, and to avoid unduly interfering with counsel in the conduct of the case at bar, the practice has become universal, and is recognized in the decisions and text writers, of permitting any medical man who has a license to practise his profession, to testify as an expert, and to give his opinion as such on any question cognate to his profession. This is so without regard to the amount of study and experience he may have had in the particular matter under consideration. The naked fact that he is licensed to practise is enough. He then—that is, after testifying that he is a practising physician—is clothed with the garment of authority. The only way in which his knowledge can be tested is by cross-examination as to his experience and skill, and possibly by contrasting him as he appears upon the witness-stand and his history as he gives it, with other and more or less experienced and skilful men who follow him. The rule is, that when a witness is produced to give an opinion on a medical question, he is interrogated by the counsel who produces him as to his qualifications. At this point, before he is allowed to give his opinion, it is proper and customary that the counsel upon the other side of the case should be allowed an opportunity to cross-examine as to his competency, and then the court determines whether or not he is a competent witness. If the court pronounces him competent, a hypothetical question is put to him stating the facts of the case, as the counsel interrogating him claims them to be established by the evidence, and the expert is then asked to give his opinion on the question at issue, based upon an assumption that the facts stated are truly stated. Then the opposing counsel has the right to cross-examine, and to ask his views and opinions upon the same question at issue, but assuming as true other and different facts or premises, as he claims them to be established by the evidence. This often involves a test of wit and intelligence, and of forensic acumen, between the counsel and the witness, which serves very little useful purpose, except perhaps to elucidate more strongly than has been here stated the defects of the system which now obtains. It is also not unusual, and in fact is the result of the workings of human nature, that under the manipulations of counsel skilled in cross-examination, skilled in methods of indirection in stating facts, and armed with the powerful weapon of the rule which permits them to insist upon a categorical yes-or-no answer to a question, the jury and the court become confused, the witness loses his temper, or becomes affected more strongly than ever before by bias against his persecutors, as he feels them to be, and the examination ends in a farce. This is not always the case, and the illustration given is an extreme one. Like the citations from judicial criticism of expert testimony which have been given, these matters are only adverted to here as danger signals, a warning to both professions, and with an earnest suggestion of the necessity of reform. EXPERTS, HOW SUMMONED INTO COURT. _They Must Obey the Summons and Appear and be Sworn. In General they need Not Give their Opinions unless Duly Compensated._—An expert witness is brought into court like an ordinary witness by the usual process of the court. This process is, under the American system, an ordinary subpœna, and, being process of the court, whether or not he has been paid or promised compensation for giving his opinion he must obey the process to the extent at least of appearing in court when called, to be sworn. Interesting questions have been raised as to his obedience to the subpœna to the extent of testifying when he has not been compensated. It has been argued, and the argument is sustained by the decisions of courts of high authority in some States, that his knowledge and skill, acquired by study and by experience, is his property, of which he cannot be deprived without just compensation, under his constitutional rights guaranteed to him by the organic law of this country. On the other hand, in some other States it has been held that he is so far a necessary part of the judicial system that he may be called upon to give the results of his experience, knowledge, and skill forming his opinion, without payment other than the ordinary compensation to witnesses. It is believed, however, that the better opinion is the former; that he does not stand on the same footing as an ordinary witness, whose province it is to testify solely to matters of observation of fact, but that he stands in the position of one who has something to give; something to impart in the way of knowledge or experience, which is his property as much as any other thing movable or immovable of which he is possessed. A somewhat different question has arisen in the case of a witness who, like a family physician or attending physician, has learned facts and has been paid for his attendance, or who exacts payment for his attendance, as a physician from his patient, and this question is; when such a professional man has been called upon to testify to the information he thus attained, whether he can be asked for, and required to give, opinions based on those facts? Necessarily, having learned the facts by observation, such as the appearance, symptoms, and actions of the patient, he is, when testifying as to these matters, nothing more or less than an ordinary witness, because he is testifying to matters of observation. As to these matters public policy requires, except so far as it has been modified, or rather extended, by our statutes which forbid testimony as to privileged communications, that he must testify, the same as any other witness. But suppose that, having so testified to the facts, he is asked to give his opinion; for example, in an insanity case, whether the symptoms that he found in his patient led him to the belief as a professional man of experience and skill that his patient was sane or insane. The question is, Can he be compelled to give that opinion, if he chooses to decline to give it without the promise or assurance of further compensation than the mere _per diem_ fee and mileage of an ordinary witness? The best authority is to the effect that he must so testify, the reasoning of the court being that his opinion is only a part of what he derived from his original relation of physician to his patient. Wright _v._ The People, 112 Ill., 540; same case, 33 Alb. L. J., 79. _Same Rule in Civil and Criminal Cases._—The rule is the same whether the professional man is called to testify as an expert in civil or criminal cases. In either one he is not obliged to give an opinion as such, independent of a personal knowledge of the facts in the case, without being paid or assured reasonable compensation therefor. His proper course of conduct is, when he has obeyed the subpœna and is in the presence of the court and has been sworn, and the questions put by counsel disclose that the object of his examination is to elicit from him an opinion, to state to the court that he has not been paid any other compensation than that of an ordinary witness, and that he respectfully declines to give an opinion in the case as an expert, without compensation proportionate to the value of his opinion.[182] _Whether Witness Competent a Question for Court in Limine._—After the expert is placed upon the stand, as we have seen, the counsel upon the side of the case by which he is summoned interrogates him as to his capacity, the purpose of the interrogation being that his answers shall qualify him and show him to be an expert. Whether or not he is an expert so as to permit the giving of his opinion as part of the case to go to the jury, is for the court to decide _in limine_, that is, at the threshold, and as a matter of discretion, and the exercise of that discretion, if fair and reasonable, will not be disturbed upon appeal by the higher court. It is permissible, but also discretionary, after the counsel calls the witness and has apparently qualified him, for the counsel upon the other side to cross-examine the witness as to his qualifications before he is examined in chief, with a view of determining whether or not there are limitations upon those qualifications which should prevent the court from permitting him to testify as an expert. The general rule is as stated by Greenleaf in his work on Evidence, Sec. 440, that it is not necessary that the medical expert should have actually practised his profession. Nor is it essential that the witness should belong to any particular school of medicine. The law does not undertake to pass upon conflicting theories of medical practice, in determining the question of the qualification of a medical expert. It is proper, however, for counsel to inquire as to what school of medicine the witness is an adherent, because of its importance in weighing the value of his testimony after it has been given. _Persons Not Duly Licensed Sometimes Held Not Competent._—It has also been a mooted question in those States where it is necessary, in order to enable a person to practise physic or surgery, that he should be licensed, whether a person practising without a license, however extensive his reading and practice, would be considered qualified as an expert witness in a court of justice. This point, so far as diligent examination discloses, has not been determined in any reported case, although it has been suggested at _nisi prius_ and has been, in one instance within the knowledge of the writer, decided that he is not to be considered an expert in matters involving medical knowledge and skill. The reasoning of the court was that the policy of the State is to prohibit persons not possessing the qualifications required to obtain a license, from acting in any capacity as professors and practitioners of medicine or surgery. If the witness is a member of the profession, legally qualified as such, it has been held that he is sufficiently qualified as an expert if he shows that he possesses the average ability of members of his profession. Hall _v._ Costello, 48 N. H., 176; Tellis _v._ Kidd, 12 Ala., 648; Wharton on Evidence, Sec. 446; Rogers on Expert Testimony, Secs. 17 and 18; Slocovich _v._ Orient Mutual Ins. Co., 108 N. Y., 56. As to the question whether it is necessary that the witness should actually have practised his profession, see the last-cited text-writer, Secs. 43 and 44, who seems to have entertained views opposite to those stated by Professor Greenleaf. Wharton on Evidence, Sec. 439, states the rule as follows: “He must have special, practical acquaintance with the immediate line of inquiry more than a mere vague, superficial knowledge. But he need not be acquainted with the _differentia_ of the specific specialty under consideration.... A general knowledge of the department to which the specialty belongs would seem to be sufficient.” _Interested Persons may still Testify as Experts._—Since the law forbidding interested persons from being witnesses has been changed, it has been suggested that an interested person although otherwise qualified might not be a competent witness to give an opinion as an expert. But the established doctrine is that he may give such an opinion; the weight of it, however, would be for the jury to determine. Greenleaf on Evidence, Redfield’s edition, Sec. 440, citing Lockwood _v._ Lockwood, 2 Curtis, 309; Dillon _v._ Dillon, 3 Curtis, 96, 102. See also Dickinson _v._ Fitchburg, 13 Gray, 546. _Testimony of Expert, how Impeached._—Sometimes, on cross-examination or otherwise, the fact becomes known that the witness who is proposed as an expert has expressed an opinion on the subject in hand contrary to that which he has given upon the witness-stand, and the question has been raised as to establishing that fact at the outset and before his testimony goes before the jury, in order to enable the trial judge to determine whether he is competent. The rule in that case is that the testimony as to his prior expression of opinion is not to be received at that time, but will come properly up as rebuttal, he having been asked upon his cross-examination, giving time and place, whether he has made the statements attributed to him. An expert witness may in other respects be impeached like any other witness, that is, by the oaths of persons who know him and have known his reputation, and who testify that his reputation for truth and veracity is bad and that they would not believe him under oath. He may also be impeached by producing witnesses to prove that his special knowledge or technical skill is not reliable or adequate to the undertaking which he has assumed. But this testimony must be from personal knowledge of the man and not from general reputation. Wharton on Evidence, Sec. 437; Le Rose _v._ Commonwealth, 84 Pa. St., 200.[183] _General Rule as to Required Amount of Skill and Experience Stated._—The general rule may be stated thus, as derived from these and other authorities: The extent of the previous study and investigation, and the amount of skill and information which must be shown, will depend upon the facts of each particular case. But some special and peculiar knowledge or skill must be established, the amount of it to be determined by the trial judge in his discretion. The possession of such knowledge and skill is presumed in medico-legal cases if the witness is a licensed practitioner. _Some Practical Suggestions as to Conduct of Witnesses on the Stand._—In this preliminary examination, the conduct and demeanor of the witness are of no little importance, because it is then and there that he makes his first impression upon the court and jury. He should be perfectly open and unreserved in stating his means of special information, in explaining what are the limits of his personal experience and the extent of his reading; but, at the same time, it would be well for him to avoid all appearance of self-glorification and all tendency to exaggerate his individual acquirements. Often has it occurred that expert witnesses of undoubted capacity and honesty, who are unfortunately grandiose and self-assertive in their manner, have, however honest and able they might be, lost entirely their weight with the court and jury by undue self-complacency and exaggeration of their personal qualifications, during their preliminary examination. This is a matter requiring tact and judgment and nerve, and should be fully understood between counsel calling him and the witness, before the witness is placed upon the stand. In that event, it will be quite safe for the witness to closely follow the questions of counsel by his answers, and to volunteer little or nothing. If his answers are not full and complete enough, counsel can renew the question in the same or in other form or carry the matter into greater detail. If, on the other hand, his answer is too full or he appears too eager, he may create a prejudice against him which nothing can overthrow, and which the art of counsel upon the other side in cross-examination and in making comments upon his testimony when summing up before the jury, will very effectually use to destroy his weight as an expert.[184] _Scope and Extent of Examination of Expert Witnesses._—Having stated how experts may be summoned and qualified, it remains to consider the scope and extent to which they may be examined. The advancement of the sciences and the progress of research in special fields of knowledge have made expert testimony of large importance during the present century. The basis of its admission is the fact that there are certain processes of reasoning which an ordinary jury is incapable of performing, even with the assistance of courts and lawyers. Oftentimes in the administration of justice in our courts, proof is given of circumstances which although admitted would have little or no significance in the mind of an ordinary juror, and which he would be unable to contrast and compare with other facts, successfully, without the aid of those more familiar with scientific matters and the inductive process of reasoning than he is. In such cases it is necessary that the jury should be specially enlightened by persons who have, through training, skill and experience, acquired the power to enlighten them. A common instance and illustration of this matter is to be found in the case of homicide by poisoning. A human body is found dead; externally there may be no _indicia_ to show positively the cause of death. Under such circumstances the laws of all civilized countries permit what is called a post-mortem examination by skilled physicians, who, finding no external evidences of the cause of death, are permitted by the officers of the law to remove the internal portions of the body for special and careful examination. If this discloses traces of inflammation or of lesions of an abnormal character, further power is vested in the authorities to have at the expense of the State a chemical examination of the internal organs. If this examination, which is necessarily long and excessively technical, results in the discovery of any poisonous substance, such as would produce death, and if it is found in sufficient quantities to produce death, these persons who made the post-mortem examination and discovered the outward indications of the administration and effects of the poison, and the chemists who discovered the poison itself in the tissues of the body, in sufficient quantities to produce death, are called as experts before the jury. The post-mortem examiners explain what the appearance of the body was, as distinguished from the appearances of the body of an individual who had died from natural causes. The chemist describes his course of experimentation, the various deductions which he made from his experiments, the tests which he applied in his investigation in discovering poison, and is then allowed to testify that the poisonous substance was found in sufficient quantities to produce the physical appearances which the post-mortem examiners have described, and to accomplish the death of the human being in whose body the poison was found. It is obvious that the power of observation and the skill, which the skilled chemists and physicians used as the basis of their reasoning in this case, were such as an ordinary man, unskilled and inexperienced, would not possess, and the ability to use them must have come from the study of treatises on such subjects, and from teaching and experience, to such an extent as to entitle the persons so testifying to be considered by the courts as qualified to express an accurate and sound opinion on the matters and things under investigation. Thus it appears how, in such cases, a departure became essential to the successful administration of justice, from the strict rule that witnesses shall testify solely to matters of fact and observation, and why it has long been considered that some witnesses must be allowed to testify to opinions and conclusions. Again, in a like case, a body is found bearing evidences of wounds or bruises. The question to be determined is whether they were inflicted before or after death; if before death, whether they were sufficient to cause death. Some wounds and injuries might be sufficiently apparent and dangerous so that the common, inexperienced eye would at once detect that they were sufficient to cause death. But in most instances this is not the case, and in such instances the testimony of experts is required by the necessity of the case, to show that the wounds and injuries were sufficient to cause death. _The General Rules Stated as to Subjects for Expert Testimony._—Hence the general rule is, that wherever the facts to be investigated are such that common experience and knowledge of men do not enable them to draw accurate conclusions, but are such that the study and experience of specialists do enable such specially endowed persons to draw accurate conclusions, then the inferences and deductions they have drawn can be testified to by those who qualify themselves before the court as persons having sufficient skill and experience as such specialists to entitle them to give opinions. The cases in which expert testimony is permitted to be given are set forth in Rogers on Expert Testimony, Sec. 6, quoting from Jones _v._ Tucker (41 N. H., 546), as follows: “1. Upon questions of science, skill, or trade, or others of like kind. “2. Where the subject-matter of inquiry is such that inexperienced persons are unlikely to prove capable of forming a correct judgment without such assistance. “3. Where the subject-matter of investigation so far partakes of the nature of science as to require a course or previous habit of study in order to the attainment of knowledge of it.” So also Chief Justice Shaw of the Supreme Court of Massachusetts, in New England Glass Co. _v._ Lovell (7 Cushing, 319), said: “It is not because a man has a reputation for sagacity and judgment and power of reasoning that his opinion is admissible in testifying as a witness. If so, such men might be called in all cases to advise the jury, and it would change the mode of trial; but it is because a man’s professional pursuit, or his peculiar skill and knowledge of some department of science not common to men in general, enable him to draw inferences where men of common experience, after all the facts have been proved, would be left in doubt.” To the same effect see Muldowney _v._ Illinois Central R. R. Co., 36 Iowa, 472; Wharton on Evidence, Sec. 436; Greenleaf on Evidence, Sec. 441. _Qualifications of this General Rule._—The extent to which an expert witness can go in giving his opinion is limited to matters of science and skill, and does not extend to the expression of views on matters of legal or moral observation, or the manner in which others would probably be influenced if the parties had acted in one way rather than in another. Campbell _v._ Richards, 5 B. & Ad., 345. So it has been held that the question whether a physician has honorably and faithfully discharged his duty in a given case, either to his medical profession or to his patient, is not a question of science but of pure ethics, upon which the jury is as competent to decide as any one else, and in such a case an opinion would not be allowed to be given either by another medical practitioner or by a professor in the science of morals. Rogers on Expert Testimony, Sec. 11, citing Ramadge _v._ Ryan, 9 Bing., 333. There are also some matters of fact which apparently transcend the dividing line between common experience and judgment and scientific experience and judgment, as to which expert testimony is not receivable, but the jury and court must weigh the facts and draw the inferences for themselves. An interesting example of this is found in the case of Manke _v._ The People, 78 N. Y., 611 (17 Hun, 410), cited in Stephens’ “Digest of the Law of Evidence,” p. 107, note H, decided in the New York Court of Appeals a few years ago. In that case one Adolf was killed by a gunshot, and pieces of paper were found near the scene of the homicide bearing certain marks. An expert was called upon to say whether they were powder-marks, and whether the condition of the paper was such that in his opinion it was wadding which had been fired from a gun. This evidence was held to be inadmissible by the General Term of the Supreme Court, and this decision was affirmed by the Court of Appeals. These courts held that the question as to whether this was a wad fired from a gun was a matter which the jury was as competent to judge of as the witness. In delivering the opinion at General Term, Presiding Justice Talcott said that this case was very close to the border line, but in his judgment it was beyond the province of experts and within the province of jurors. Nevertheless, in that case the evidence of chemists who had examined the wadding, and had discovered the marks on it which were said to be powder-marks, and upon analysis had determined that they were powder-marks, or that they were marks of powder which had exploded, would have been clearly admissible. The subjects concerning which medical men may be called upon to testify as experts are as numerous as the diseases, injuries, mental and physical conditions of the human race which fall within the range of the practice of medicine and surgery. It is therefore practically impossible to give them in detail.[185] _Practical Suggestions and Admonitions Embodied in Rules._—It is deemed advisable that the following practical suggestions and admonitions to physicians, concerning their duties as expert witnesses, shall here be given. First: A physician should refuse to testify as an expert unless he is conscious that he is really qualified as an expert. Second: After accepting the responsibility, his first duty should be to make a diligent examination and preparation for his testimony, unless it is upon a subject with which he is familiar and which he is satisfied that he has already exhausted, by reading the best authorities that he can find, and by careful reflection upon particular questions as to which his opinion will be asked. Third: Where he is to make an examination of facts, such as the post-mortem examination of a body, a chemical analysis or an examination of an alleged insane person, he should insist upon having plenty of time and full opportunity for doing his work thoroughly. He should take particular pains to make his examination open and fair, and, if possible, should invite opposing experts to co-operate with him in it. Fourth: He should be honest with his client before the trial in advising him and giving him opinions, and upon the trial should preserve an absolutely impartial attitude, concealing nothing, perverting nothing, exaggerating nothing. Fifth: On the preliminary examination as to his qualifications as a witness he should be frank and open in answering questions. He should state fully the extent and the limits of his personal experience and of his reading upon the subject, without shrinking from responsibility, yet without self-glorification. Sixth: He should be simple, plain, and clear in his statement of scientific facts and principles, avoiding the use of technical language, and trying to put his ideas in such form that they will be grasped and comprehended by men of ordinary education and intelligence. Seventh: He should avoid stating any conclusions or principles of which he is not certain, but having an assurance that he is right he should be firm and positive. He should admit the limitations of his knowledge and ability. Where a question is asked which he cannot answer, he should not hesitate to say so; but he should refuse to be led outside the subject of inquiry, and should confine his testimony to those scientific questions which are really involved in the case, or in his examination of the case. Eighth: And finally, he should always bear in mind that at the close of his testimony an opportunity is usually given to him to explain anything which he may be conscious of having said, which requires explanation; and partial statements which need a qualification to make them a truth. This is the physician’s opportunity to set himself right with the court and with the jury. If the course of the examination has been unsatisfactory to him, he can then, by a brief and plain statement of the general points which he has intended to convey by his testimony, sweep away all the confusion and uncertainty arising from the long examination and cross-examination, and can often succeed in producing for the first time the impression which he desires to produce, and can present the scientific aspects of the case briefly and correctly. Probably no man was ever so gifted as to be able in practice to carry out all of these principles in giving medical testimony. If he could, he would be the ideal expert witness. But the principles are, after all, simple and easily followed in the main. Any physician who knows his subject and who has a clear head and the ordinary faculty of expression, by observing these principles can make himself invaluable as an expert witness. There is no branch of the profession which brings a broader fame, greater influence, or larger emoluments than this. There is no branch, on the other hand, in which men of real ability make more lamentable failures.