Taylor, in his well-known work on “Medical Jurisprudence,” lays down many valuable suggestions for the guidance of medical witnesses; among other things, he says, “In reference to facts, a medical witness must bear in mind that he should not allow his testimony to be influenced by the consequences that may follow from his statement of them, or there probable effect on any case which is under trial. In reference to opinions, their possible influence on the fate of a prisoner should inspire caution in |107| forming them; but, when once formed, they should be honestly and candidly stated, without reference to consequences.” “The questions put on either side should receive direct answers from the medical witness, and his manner should not be perceptibly different whether he is replying to a question put by the counsel for the prosecution, or for the defence.” “The replies should be concise, distinct and audible, and except where explanation may be necessary, they should be confined strictly to the terms of the question.” “Answers to questions should be neither ambiguous, undecided, nor evasive.” “The replies should be made in simple language, free from technicality.” “A medical witness may, without any imputation upon his bona fides, explain medical points to counsel, and correct him on medical subjects, when wrong in his views or statements, but he should avoid even the appearance of prompting counsel in the conduct of the case.”
CHAPTER VIII. MEDICAL EXPERTS.
Whenever the subject matter of a legal enquiry is such that, from its partaking of the nature of a science, art or trade, inexperienced persons are unlikely to prove capable of forming a correct judgment upon it without assistance, then the opinions of witnesses possessing peculiar skill and knowledge in the matters in question are admissible in courts of justice. And it is only when the matter inquired of lies within the range of the peculiar skill and experience of the witnesses, and is one of which the ordinary knowledge and experience of mankind does not enable them to see what inference should be drawn from the facts, that the skilled witnesses may supply opinions as their guide ([267]). The rule admitting the opinions of experts in such cases is founded on necessity, for juries are not selected with any view to their knowledge of a particular science, art or trade, requiring a course of previous study, experience or preparation ([268]).
The rule of law on which the giving in evidence the opinion of witnesses, who know nothing of the actual facts of the case, is founded, is not peculiar to medical testimony, but is as a general rule applicable to all cases where the question is one depending on skill and science in any particular department. . . . In general it is the opinion of the jury which is to govern, and this is to be formed upon the |109| proof of the facts laid before them. But some questions lie beyond the scope of the observation and experience of men in general, yet are quite within the observation and experience of those whose peculiar pursuits and profession have brought that class of facts frequently and habitually under their consideration. When, therefore, a question arises in a court of justice upon any such subject, and certain facts are proved by other witnesses, one skilled in such subject may be asked his opinion as to the character of such facts; or he may be asked his opinions on certain facts observed by himself. This is true with regard to any question of science, because persons conversant with such science have peculiar means, from a larger and more exact observation and long experience in such department of science, of drawing correct inferences from certain facts observed by themselves or testified to by other witnesses. The opinion of such witnesses is designed to aid the judgment of the jury in regard to the influence and effects of certain facts which lie out of the observation and experience of persons in general ([269]). These witnesses are called “experts.” This term seems to imply both superior knowledge and practical experience in the art or profession. But generally nothing more is required to entitle one to give testimony as an expert, than that he has been educated in the particular art or profession; for persons are presumed to understand questions pertaining to their own profession or business ([270]).
The practice of admitting the evidence of experts is an old one: in the Roman Law they are frequently alluded to, and in the earliest Common Law reports they are spoken of as of established usage. Says Saunders, J., “and first I grant that if matters arise in our law which |110| concern other sciences or faculties we commonly apply for the aid of that science or faculty which it concerns. In a case of mayhem the defendant prayed the court that the wound might be examined, on which a writ was issued to the sheriff to cause to come “medicos chirurgos de melioribus London. ad informandum Dominum regem et curiam de his quæ eis exparte Domini Regis injungerentur ([271]).”
Some Judges and writers have very little respect for the evidence and opinions of experts. An Iowa Judge says, observation and experience “teach that the evidence of experts is of the very lowest order, and of the most unsatisfactory kind.” One from Maine, speaks of “the vain babblings and oppositions of science so called, which swell the record of the testimony of experts when the hopes of a party depend rather upon mystification than enlightenment.” An Illinois Judge quotes a distinguished occupant of the bench as saying, “if there was any kind of testimony not only of no value, but even worse than that, it was in his judgment that of medical experts.” Lord Campbell said, “Hardly any weight is to be given to the evidence of what are called scientific witnesses: they come with a bias on their minds to support the cause in which they are embarked” ([272]). Taylor says, “Perhaps the testimony which least deserves credit with a jury is that of skilled witnesses. . . . Being zealous partisans their belief becomes synonymous with faith as defined by the apostle, and it too often is but the substance of things hoped for, the evidence of things not seen” ([273]). On the other hand, Best says, “It would not be easy to overrate the value of the evidence given in many difficult and delicate enquiries, not only by medical men and physiologists, but by learned |111| and experienced persons in various branches of science, art and trade” ([274]). And many Judges have spoken of the essential aid to courts and juries rendered by the opinion of the experienced, skilful and scientific witness who has a competent knowledge of the facts involved.
When one takes his place as an expert before a court, a legal paradox is instituted on his behalf, by which he is allowed to testify—not as to what he knows, but to what he believes or forms an opinion upon, based necessarily on probabilities of analogy as well as experience. Nothing is required (in the absence of any statutory provision to the contrary) to entitle any one to give evidence as a medical witness, than that he has been educated in the science of medicine; and this he may be by study without practice, or by practice without study; it is not necessary that he should be a physician, or have studied for one, nor be a graduate, nor one licensed to practise, nor need he be or have been a practitioner ([275]). One may be competent to testify as an expert, although his special knowledge of the particular subject of enquiry has been derived from the reading and study of standard authorities, and not from experience or actual observation. But one cannot qualify himself as an expert in a particular case merely by devoting himself to the study of authorities for the purposes of that case, when such reading and study is not in the line of his special calling or profession and is entered upon to enable him to testify in the case. In Vermont, however, it has been held that mere education as a physician, without some practice as such, is insufficient to qualify one as an expert; and in Arkansas, it is said, that competency must be shewn from study and experience. In New York, it has been held that one otherwise qualified, who is |112| a physician and surgeon, may give evidence, although not in full practice at the time; this fact merely goes to affect his credit ([276]).
It is not necessary that the physician should have made the particular disease involved in the enquiry a specialty; medical men of practice and experience are experts, and their opinions are admissible in evidence upon questions that are strictly and legitimately embraced in their profession and practice. If one has made the matter in question a specialty, doubtless his opinion will be of more value than if he has not; and it has been said, that one who has devoted himself exclusively to one branch of his profession cannot give evidence as an expert on another ([277]). For example, one not an oculist may speak as to the cause of injuries to an eye; one who has not made diseases of the mind a special study may give his opinion as to the existence of insanity; one not a practical chemist or analyst, but understanding the practical details of chemistry and the means of detecting poisons, may testify as to the tests in the chemical analysis of a stomach, and as to the tests usually applied to detect poison ([278]). The law will even allow a physician to speak as to the length of time a mule has been suffering from a disease ([279]). But one who has had no experience as to the effect upon health of illuminating gas cannot testify in relation thereto as an expert ([280]). Nor can one who has for thirty years been exclusively treating the insane be permitted to testify, as an expert, on |113| the mental capacity of a person in the last stages of disease, who has not been previously insane ([281]).
To render the opinion of a witness competent evidence, he must, in general, be in some way peculiarly qualified to speak on the subject, and have knowledge not possessed by the mass of persons of ordinary experience and intelligence ([282]). Upon this principle, a priest who had studied physiology and psychology, in order that he might pass upon the mental conditions of communicants in his church, and who had so to decide daily, was permitted to speak as to the mental state of a woman whom he had attended in her last illness ([283]).
It is a question of fact to be decided at the trial, by the Court, whether a witness offered as an expert has the necessary qualification ([284]). And the matter cannot be referred to the decision of the jury. The decision of the Judge at the trial will not be interfered with by the Court, except in a clear and strong case ([285]).