So long as the ordinary ideal of punishment prevails, a crime must consist of an act coupled with an intent to do the thing, which probably means an intent to do evil. This is no doubt the right interpretation of intent, although cases can be found, generally of a minor grade, which hold that evil intent is not necessary to the crime. Under the law as generally laid down, insanity is a defense to crime when the insanity is so far advanced as to blot out and obliterate the sense of right and wrong or render the accused unable to choose the right and avoid the wrong. Of course, legal definitions of scientific terms, processes, or things, do not ordinarily show the highest wisdom. It is safe to say that few judges or lawyers have ever been students of insanity, of the relation of "will" to "conduct," or of other questions of science or philosophy. Each man confines himself to his field of operation, and the love of living does not induce him to go far from the matter in hand, which to him means the base of supplies.  
The insane are exempted from punishment for crime on the ground that they are not able to prepare and attend to their cases when placed on trial and on the further ground that their "free will" is destroyed by disease or "something else," and therefore they could form no intent. In another place I have tried to point out the fact that the acts of the sane and the insane are moved by like causes, but this is not the theory of the law.
 
Insanity is often very insidious. Many cases are easily classified, but there is always the border line, the twilight zone, which is sure to exist in moral questions and in all questions of human conduct, and this is hard to settle. It is generally determined by the feelings of a jury, moved or not by the prejudice of the public, depending on whether the community has been lashed or persuaded to take a hand in the conduct of the case.
 
Lawyers and judges are not psychologists or psychiatrists, neither are juries. Therefore the doctor must be called in. As a rule, the lawyer has little respect for expert opinion. He has so often seen and heard all sorts of experts testify for the side that employs them and give very excellent reasons for their positive and contradictory opinions, that he is bound to regard them with doubt. In fact, while lawyers respect and admire many men who are expert witnesses, and while many such men are men of worth, still they know that the expert is like the lawyer: he takes the case of the side that employs him, and does the best he can. The expert is an every-day frequenter of the courts; he makes his living by testifying for contesting litigants. Of course scientific men do not need to be told that the receipt of or expectation of a fee is not conducive to arriving at scientific results. Every psychologist knows that, as a rule, men believe what they wish to believe and that the hope of reward is an excellent reason for wanting to believe. It is not my intention to belittle scientific knowledge or to criticise experts beyond such general statements as will apply to all men. I have often received the services of medical experts when valuable time was given without any financial reward, purely from a sense of justice. But all men are bound to be interested in arriving at the conclusion they wish to reach. Furthermore, the contending lawyers are willing to assist them in arriving at the conclusions that the lawyer wants.
 
It is almost inevitable that both sides will employ experts when they have the means. The poor defendant is hopelessly handicapped. He is, as a rule, unable to get a skillful lawyer or skillful experts. A doctor's opinion on insanity is none too good, especially in a case where he is called only for a casual examination and has not had the chance for long study. The doctor for the prosecution may find that the subject can play cards and talk connectedly on most things, and as he is casually visiting him for a purpose, he can see no difference between him and other men. This may well be the case and still have little to do with insanity. Experts called for the defense cannot always be sure that the patient truthfully answers the questions. A doctor must make up his mind from examining the patient, except so far as hypothetical questions may be used. In all larger cities, certain doctors are regularly employed by the prosecution. While it would be too much to say that they always find the patient sane, it is saf............