The intelligent study of mental disease by medical men has resulted in its being detected at so early a stage and in such a mild form that its proper treatment might almost be called, when successful, the prevention of insanity. Cerebro-mental disease, though it be only in its incipient form, implies to the physician the necessity for medical treatment; but it {103} is another question whether the disease is sufficient in amount to impair the power of self-control and will so as to determine irresponsibility. It is not the doctor's province to punish for crime, but to treat for disease, and he often forgets that fact. The various medical definitions of insanity in textbooks and on the witness-stand do not clearly enough state how far the medical and how far the forensic meaning of the word is implied. What seem to be wide differences of opinion regarding responsibility for crime, as given in the courts, are often due to different ways of stating the question, and nothing more. Boileau said that all men are insane, the only difference between them being the varying degrees of skill with which they are able to conceal the crack; and Montesquieu, that insane asylums are built in order that the outside world may believe itself sane. In 1832, Haslam, one of the first experts in mental disease in England at that time, testified in court that he had never seen a sane man in his whole life, adding, “I presume the Deity is of sound mind, and He alone.” It is impossible to give a satisfactory definition of insanity, to draw any hard and fast line on one side of which we should put all the sane, and on the other all the insane. It is not possible to divide insanity from sanity by a single criterion, such as the existence of delusions, inasmuch as many sane people have very curious delusions; for instance, Sir William Blackstone's belief in witchcraft, as stated in his _Commentaries on the Laws of England_; Martin Luther's assertion that he saw the devil and threw an inkstand at him at a time when a belief in a personal devil was required by the canons of the Church of England; Napoleon's faith in his star; the common belief of the French generals that Joan of Arc's hallucinations were divine messages. Insane delusions have been defined as false beliefs, impossible from the nature of things or the circumstances of the case, according to general belief. One can only judge of each case and each person by the conditions attending them. A belief consistent with one person's whole life and character might indicate such a change in another as to be a mark of insanity.