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].