If the patient has no reason for simulation, it is commonly best to tell him the object of the examination. The family history should be learned from others, as questioning the patient on these points is apt to put him in a train of thought unfavorable to a hopeful view of his own case. After full personal questions concerning himself and his environment, one can usually tell whether there are unreasonable suspicions, violent impulses, perverted feelings with regard to his family, delusions, hallucinations, or illusions. A delusion's existence must often be accepted, however, from the behavior of the patient and from the statements of those about him. Hallucinations of hearing must sometimes be inferred from the attitude of listening to imagined voices; and prolonged observation under circumstances such that the patient does not know that he is watched will often settle the question of his insanity when other means have failed. A careful examination should, of course, be always made for the physical and rational signs of disease. In the differential diagnosis care must be used not to mistake for insanity the acute diseases typhoid fever, meningitis, smallpox before the period of eruption, pneumonia, cerebro-spinal meningitis, narcotism or delirium from drugs, and alcoholism—errors which have been made, and which can be avoided by deferring one's opinion for a sufficient time. The detection of simulation is more difficult, especially as the insane sometimes feign insanity for a purpose, or, on the other hand, accuse themselves of wrong acts which they never committed. In general, it may be said that sane persons pretending to be insane very much overdo their part, do not make their symptoms conform to any recognized type of disease, and have a strong motive for their deception, as well as for the act for which they wish to be considered irresponsible. Their insanity first appears after the deed; they are exhausted by their efforts to seem mad, and appear quite sane if watched when they think that they are unobserved. A crime performed without accomplices, with no plan or a silly one for escape, and with no sane motive, is usually itself evidence of insanity. On the other hand, people partly demented by chronic insanity often commit crimes with all the method and motive of the criminal. In not a few cases, especially when the fact or not of impaired intellect cannot be decided by comparison with a previous condition, the question of {125} insanity, or at least of responsibility, will be beyond human wisdom. A correct diagnosis can, of course, not be made without a familiarity with the various forms of mental disease; and insanity is now so well understood that a sufficient examination of an insane person should develop the clinical history of some known type of disease in nearly every case.