The opinion evidence of medical men in questions of insanity is not, as a rule, looked upon with any very great degree of favor by the courts who have to decide upon the competency, relevancy and weight of the opinions uttered. Chapman, C.J., of Massachusetts, in charging a jury said, “While they afford great aid in determining facts, it often happens that experts can be found to testify to anything however absurd” (313). In another insanity case another Judge remarked, “Experience has shown that opposite opinions of persons professing to be experts may be obtained to any amount, and it often occurs that not only many days but many weeks are consumed in cross-examinations to test the skill and knowledge of such witnesses, and to test the correctness of their opinions,” (this was the case to a great degree in the well known Guiteau prosecution,) “thus wasting time and wearying the patience of both Court and jury, perplexing, instead of elucidating, the question involved in the issue” (314). As to the perplexing instead of elucidating, a writer of the highest authority gives the following, “In a case of alleged child murder a medical witness, being asked for a plain opinion of the cause of death, said, that it was owing to ‘atelectasis and a general engorgement of the pulmonary tissue’.” And in a trial for an assault a "122" surgeon, in giving his evidence, informed the Court “that on examining the prosecutor, he found him suffering from a severe contusion of the integument under the left orbit, with great extravasation of blood and ecchymosis in the surrounding cellular tissue, which was in a tumefied state, and there was also considerable abrasion of the cuticle.” The Judge said, “You mean, I suppose, that the man had a bad black eye.” “Yes.” “Then why not say so at once” (315).

Redfield, C.J., in his book on Wills, says, “Experience has shown both here and in England that medical experts differ quite as widely in their inferences and opinions as do other witnesses. This has become so uniform a result with the medical experts of late that they are beginning to be regarded much in the light of hired advocates, and their testimony as nothing more than a studied argument in favor of the side for which they have been called. So uniformly has this been proved in our experience that it would excite scarcely less surprise to find an expert called on one side testifying in any particular in favor of the other side, than to find the counsel upon either side arguing against their clients and in favor of their antagonists” (316).

A Lord Chancellor once remarked that his experience taught him that there were very few cases of insanity in which any good came from the examination of medical men. Their evidence sometimes adorned a case, and gave rise to very agreeable and interesting scientific discussions, but after all they have little or no weight with the jury. And Mr. Justice Davis, of the Supreme Court of Maine, after stating that he thought juries far more trust-worthy than experts on the subject of insanity, said, “if there is any kind of testimony that is not only of no value but "123" even worse than that, it is in my judgment that of medical experts. They may be able to state the diagnosis of the disease more learnedly, but upon the question whether it had, at a given time, reached such a stage that the subject of it was incapable of making a contract, or irresponsible for his acts, the opinion of his neighbors, if men of good common sense, would be worth more than that of all the experts in the country” (317). There is scarcely a single hypothesis as to responsibility (on the part of the insane), no matter how wild, which, among the large number of experts who have concerned themselves with this branch of study, has not its advocates. So says Wharton in his valuable treatise on Mental Unsoundness (318); or as Cicero elegantly put it long ago, “nihil tam absurde dici potest, quod non dicatur ab aliquo philosophorum” (319).

Considering these things, one is not surprised at Campbell, C.J., in the Bambridge case, saying to three medical men who had recorded their opinions in favor of the insanity of the testator: “You may go home to your patients, and I wish you may be more usefully employed there, than you have been here;” and to the jury he remarked, “We have had during the trial the evidence of three medical witnesses, and I think they might as well have stayed at home and attended to their patients.”

On the other hand, Shaw, C.J., said, “such opinions (as to sanity, etc.) when they come from persons of experience, and in whose correctness and sobriety of judgment just confidence can be had, are of great weight, and deserve the respectful consideration of a jury. But the opinion of a medical man of small experience, or of one who has crude and visionary notions, or who has some favorite theory to "124" support is entitled to very little consideration. The value of such testimony will depend mainly upon the experience, fidelity and impartiality of the witness who gives it” (320). And Chief Justice Gibson speaks with just emphasis of the the deference due, in their own department, to the knowledge obtained by men of a subject with which they have grappled all their lives (321). The Supreme Court of Texas declared, “The opinions of medical men (on questions of insanity) are received with great respect and consideration, and properly so.” The Supreme Court of Pennsylvania says, “It is well settled that the knowledge and experience of medical experts is of great value in questions of insanity.” Equally strong are the utterances of the Court of Appeals of West Virginia and the Supreme Court of North Carolina (322).

Where the point in question is the sanity of a person, the opinion of a medical man on the subject is, of course, admissible when that opinion is drawn from personal observation. This is the rule both in England and the United States (323). But a medical man may also give his opinion on this subject, even though he has no knowledge of the person whose sanity is in question (324). It has been suggested, that when a physician is asked his opinion on the facts stated by other witnesses, he should be first examined as to the particular symptoms of insanity; and as to whether all or any, and which of the circumstances spoken of by the witnesses upon the trial are to be regarded as "125" such symptoms; then inquire of him whether any and what combination of these circumstances would, in his opinion, amount to proof of insanity (325).

It has been held to be improper to ask a medical witness whether the person, whose sanity was in question, possessed sufficient capacity to make a will, or to transact business, as these are matters of law, depending on the nature of the business (326). In England such witnesses can only speak as to the state of mind, not as to the responsibility of a prisoner; this latter point is for the jury under the direction of the Judge (327). So, on the plea of insanity at the time of making a contract, the opinion of the medical man who gave the certificate on which the defendant was confined as insane at or about the time, is only evidence for the jury, who must judge of the grounds upon which it was formed (328).

In England, an expert cannot be asked, after being present at the whole trial, whether the defendant was insane, or whether the act complained of was an insane act, because these are questions for the jury and the witness must not be placed in the jury’s place; but he may be asked whether such and such appearances, proved by other witnesses, are in his judgment symptoms of insanity (329). The particular facts proven by other witnesses may be taken and the expert may be asked “assuming these facts to be true, do they in your judgment indicate insanity on the part of the defendant at the time the alleged act was committed?” (330). "126"

As a rule the Court should not allow an expert to give his opinion upon facts proved by a witness unless he has heard all the testimony of the witness, because the entire testimony may be necessary in order to enable him to form an opinion in regard to the subject matter of inquiry (331).

Where the facts are disputed, experts can only be questioned as to their opinion of a party’s sanity on a hypothetical case, or as to certain designated facts existing in the case supposing them to be true (332).

The mode in which this hypothetical question is to be put has been much considered. In England, in the celebrated Macnaghten case in answer to an inquiry of the House of Lords, whether “a medical man conversant with the disease of insanity, who never saw the prisoner previously to the trial, but who was present during the whole trial and the examination of the witnesses, can be asked his opinion as to the state of the prisoner’s mind at the time of the commission of the alleged crime; or his opinion whether the prisoner was conscious at the time of doing the act, that he was acting contrary to the law; or whether he was labouring under any and what delusion at the time?” The twelve judges replied, “We think the medical man, under the circumstances supposed, cannot in strictness be asked his opinion in the terms above stated, because each of these questions involves the determination of the facts deposed to, which it is for the jury to decide, and the questions are not mere questions upon a matter of science in which case such evidence is admissible. But where the facts are admitted or not disputed, and the question becomes substantially one of science only, it may be convenient to "127" allow the question to be put in that general form, though the same cannot be insisted on as a matter of right (333).”

In Massachusetts, Chief Justice Shaw said, “The proper question to be put to the professional witness is this—If the symptoms and indications testified to by the other witnesses are proved and if the jury are satisfied of the truth of them, whether in their opinion the party was insane, and what was the nature and character of that insanity; what state of mind did they indicate; and what they would expect would be the conduct of such person in any supposed circumstances?” (334).

In another well known case, the Judge said to the jury, “It is not the province of the expert to draw inferences of facts from the evidence, but simply to declare his opinion on a known, or hypothetical state of facts, and therefore the counsel on each side have put to the physicians such states of fact as they deem warranted by the evidence, and have taken their opinions thereon. If you consider any of these states of facts put to the medical witnesses are proved, then the opinions thereon are admissible evidence, to be weighed by you, otherwise their opinions are not applicable to the case” (335).

The opinions of both experts and non-experts should have weight according to their opportunities and qualifications for examination of the state of mind of the person whose sanity is in question. First of all will be the family, or the physician who has attended the patient through the disease which is supposed to have disabled his mind; next are those who, without special learning on the subject, have had the best opportunities for judging—the members of his family and those whose intimacy in the family, have given them opportunities of seeing the patient at all times and "128" noticing the alienation of his mind; and last, come those who only occasionally and at intervals have seen him, and whose chances of studying his moods have been small (336).

It has been held, in Massachusetts, that a physician who had not made insanity a special subject, and who, when consulted in such matters, always called in a specialist, is not competent to give an opinion on an hypothetical case put to him, unless he was the person’s attending physician; then his opinion is received, as it is his duty to make himself acquainted with the peculiarities, bodily and mental, of a person who is the subject of his care and advice (337). And where a physician had for more than thirty years been exclusively treating the insane, he was not permitted to testify, as an expert, to the mental capacity of a person—not previously insane—who was in the last stages of disease (338).

One not an expert may give an opinion, founded on observation, as to whether a person is sane or insane, not­with­stand­ing the general rule, that persons not medical men cannot give their opinions as to the existence, nature or extent of disease in any one. The exception was first introduced in regard to the subscribing witnesses to a will, who were permitted to speak as to the testator’s state of mind; it has now been extended to all cases where the witness’ acquaintance with the party whose sanity is in dispute, or his means of observation, are sufficient to enable him to express his opinion as to the mental condition. The Courts of Massachusetts, Maine, New Hampshire and Texas, however, still adhere to the old rule and admit the evidence of non-experts only in cases of wills (339).