had inflicted a wound, which wound had nothing to do with the cause of death, the person causing the wound is evidently not guilty of murder. So in the supposititious case, the preliminary question for the jury to decide before coming to a conclusion as to the guilt or innocence of the accused is, whether the wound could cause death. Now, the experience of medical men is supposed, on the ground of the maxim that every person should be believed in his own art," to be the same in relation to those matters that the experience of ordinary men is in relation to matters of business; and in such a case it has been customary to summon a medical man, not merely to speak to a fact-say of the existence of the woundbut to draw an inference from the facts-say of the size, the nature, the position of the wound-either observed by himself or described to him by what he has heard in court, and to say whether such a wound could cause death.

66

2 491. Opinion on Case as Proved. But, although the opinion of witnesses founded on the case as proved by other witnesses at the trial is admissible,' it must be the opinion of a witness possessing peculiar skill, and it must be in a case in which, from the nature of the circumstances, inexperienced persons have not the means, or are unlikely to prove capable, of forming a correct judgment without assistance.' A witness not a professional expert is not competent to express a general opinion on the question whether an individual was sane or insane. Though when examined as to what he himself witnessed in regard to such individual, he may state the impression produced on his mind by what he observed," but he must state, if required, the facts from which his opinion is formed, so that the jury can judge of the value of his opinion. This witness, then, is a medical expert.

Rex v. Wright, Russ. & R. 456; Rex v. Searle, 1 Mood. & Rob. 75, per Parke, J.; Fenwick v. Bell, 1 Car. & K. 312; Beckwith v. Sydebotham, 1 Camp. 117; Collett v. Collett, 1 Curteis, 687.

McFadden v. Murdock, 1 I. R., C. L. 211.

3 O'Brien v. People, 36 N. Y. 276; Clapp v. Fullerton, 34 N. Y. 190. See also State v. Pike, 49 N. H. 399, per Doe, and authorities there cited.

Culver v. Haslam, 7 Barbour, 314; Rambler v. Tyron, 7 Serg. & Rawle, 90; Clapp v. Fullerton, 24 N. Y. 190.

2492. In what Cases Called.-In other cases medical men are summoned to give the jury the advantage of that professional skill and peculiar experience which is necessary to the due understanding of the point at issue, and to the justness of the inferences which they have to draw from the facts proved. Thus, in many cases, questions as to the causes of disease, the treatment of sickness, the precise period of death, and the presumution of survivorship, or the chance of recovery, must come before courts of law, and in such cases it has been usual to have recourse to the opinions of medical experts. In no class of cases, however, has it been so frequent to ask medical men to assist the jury to draw inferences as in cases in which the sanity or insanity of an individual was in question, and in relation to no class of cases has the admissibility of this kind of evidence been so much canvassed.

2 493.

Theory of the Admissibility of such Evidence. The theory of the admissibility of this kind of evidence seems to us to be this: The law, finding that technical knowledge was necessary in arriving at conclusions in many cases, allowed witnesses to be called to supply that technical knowledge. The true method of placing the jury in possession of the required knowledge was by tracing some of the general principles of the science without reference to the individual case. The object was to make the jurymen medical men in relation to the point at issue, yet to leave them ordinary unskilled individuals in relation to the facts of the case which were to be gauged by their own common sense and everyday experience. To do this, it was necessary to put the jury in possession of medical experience in relation to the case, but as the jury could not go through the medical man's practice or walk the hospital with him, it became usual to allow the medical man to give the jury the result of his experience quo ad the point in question, that is to say, the medical man was allowed to express an opinion.

2494. Experts not to Usurp Functions of Jury.-But one thing at once became evident, and that was, that if medical men were to be allowed to express an opinion, say as to

the sanity or insanity of an individual in a case where the question of guilt and innocence turned upon that of mental soundness or unsoundness, the functions of judge and jury would thereby become a farce. The jury would have simply to endorse the medical man's opinion, and the institution of trial by jury, which, as Burke has said, is the object of the whole British constitution, including two Houses of Parliament, King, and all the rest of it,' would be nothing more than an elaborate and ridiculous absurdity. But we do not trust the high function of decision as to guilt or innocence in any case to one man, even when he could be confronted by facts which are cognizable to the community; and it would be miserably advised to trust such a function to one medical man, when the public would not be in a position to review his decision, and when the administrators of law have, from long and intelligent experience, come to the conclusion of the general worthlessness of the evidence of experts. The real use of experts really was to explain to the jury how they might themselves come to a conclusion as to a disputed point, not to come to a conclusion for them.

2

495. New Doctrine as to Skilled Witnesses. It is true that in New Hampshire, in 1871, judicial opinions were expressed that it was the function of experts to declare what irresponsibility is. In State v. Pike, Doe, J., said: "The whole difficulty is that courts have undertaken to declare that to be law which is matter of fact. The principles of the law were maintained at the trial of the present case, where experts having testified, as usual, that neither knowledge nor delusion is a test, the Court instructed the jury that all tests of mental disease are purely matters of fact, and that if homicide was the offspring of mental disease in the defendant, he was not guilty by reason of insanity." The doctrine that responsibility is a question of fact to be determined by the jury, on the evidence of experts, has been adopted by Dr. Mauds

It was all to him, only the "method of getting twelve jurymen put into a jury box."

2 See ante § 486. See also as to experts in military practice, Bradley v. Arthur, 4 Barn. & C. 293, 305, 307, 311.

349 N. H. 399.

ley, who sees in these New Hampshire decisions "an advance upon any judgment concerning insanity which has been given in this country. They put in a proper light the relations of medical observations to law in questions of mental disease." These views are not only in conflict with all judicial authority both in this country and in America, which held and holds that although experts may be called to testify as to states of mind and conditions of health, it is for the Court to declare whether such states or conditions constitute irresponsibility, but are at variance with the true principles of reason, and have been repudiated both by jurists and physicians in America."

496. Cases in which Expert Evidence has been had Recourse to. Thus in old days it was usual to call frank inspectors who were supposed to be qualified to speak as to handwriting, and in our own time we have an expert whose skill and opinion is much respected in cases where it is necessary to discover the identity of, or differences in, written documents. But in those cases the expert not only says, "I think these are written by the same person," but he says, "I have come to that conclusion because in each of these writings the i is formed thus, and the b thus," and so on, and in this way he gives the jury the means of judging of the correctness or incorrectness of his inference. So in cases where antiquaries have been examined as to the date of a certain document, or artists as to the originality of a picture, or where an expert has been asked his opinion as to whether coins have been stamped in the same die, or whether wines have been taken from the same bin, in all these the skilled witness could give the grounds of his opinion; and if these seemed frivolous or insufficient, his evidence might be rejected by the jury."

Responsibility in Mental Disease, pp. 105, 106.

"See Wharton on Mental Unsoundness and Psychological Law, 3d ed. 1873, §§ 190, 199.

Revitt v. Braham, 4 T. R. 497; Moody v. Rowell, 17 Pick. 490; Com. v. Carey, 2 Pick. 47; Lyon v. Lyman, 9 Conn. 55; Lodge v. Phipher, 11 Serg. & R. 333.

* See Folkes v. Chadd, 3 Doug. 157.

5 Naturalists who have observed the habits of certain fish have been permitted to state their opinion as to the ability of fish to overcome particular obstructions in a

497. Expert's Opinion on Evidence Adduced. The great difficulty arose, however, when experts were asked to come to a conclusion from the evidence they had heard. In such cases, they were asked to do what the jury was there to perform. And it became necessary to frame some rule of law which would at the same time give the jury the advantage of the expert's skill and still preclude the injurious influence upon their minds of an expression of opinion-of a person who came there with a reputation for knowledge-upon the very point they had to decide. On examination, the cases will show the expedients which were devised to effect this double purpose.

2498. Questions which may be Put.-At the trial of Earl Ferrers in 1763, his counsel proposed to ask a medical witness "whether any and which of the circumstances which had been proved by the witnesses are symptoms of lunacy?" This question was objected to by the Attorney-General, and Baron Henley, observing that the question "tended to ask the doctor's opinion upon the result of the evidence," said that he "must be asked whether this or that fact is a symptom of lunacy." Here there was an effort to get at the advantage of the medical experience without the disadvantage of a decision upon all the facts proved, which was obviously a question for the jury. On the trial of McNaughton,2 an expert, who had heard the whole trial, was asked the question, "Judging from the evidence which you have heard, what is your opinion as to the prisoner's state of mind?" and it was not objected to. This question was evidently open to

river which they are accustomod to ascend. Cottrill v. Myreck, 3 Fairf. 222. It has been held that the question whether two pieces of wood were parts of the same stick of natural growth is a question for an expert. Commonwealth v Choate, 105 Mass. 451. See also Folkes v. Chadd, 3 Doug. 157; Ashby v. Lill, 5 Bing. 299.

1 19 Howell. 943. Lord Brougham, too, was of the opinion that it was well to preclude the medical witness from giving an opinion on the evidence, and regarded him only as a guide to the jury, a dictionary in which they might look and see if a certain act was an indication of insanity. You shall ask them," he says, "if such an act is an indication of insanity or not: you shall ask them, upon their experience, what is an indication of insanity. You shall draw from them what amount of symptoms constitute insanity, but you must not ask a witness whether the facts sworn to by other witnesses preceding him amount to a proof of insanity."-67 Hansard, 614. 10 Clark & Fin. 200.