Probably of greater importance than the acquired pathological conditions of the brain in producing insanity is a congenital condition in which the nervous system is defective.  The most fertile cause of insanity lies in the inheritance; by this it must not be understood that insane parents produce insane offsprings, but that conditions inherited from immediate or remote ancestors appear in a diminished resistance of the nervous system which is sooner or later expressed as insanity.  Given such a defective nervous system, extrinsic conditions which would have no effect on another individual or would be felt in different ways may produce insanity.  In these cases occupation plays a great role.  The excitement and privations of war especially in the tropics and the ennui of camps leads to insanity in soldiers; occupations such as that of the baker in which there is loss of sleep and the mental strain of students can all act in the same way.  A woman who gives no sign of nervous defect may become insane under the strain of pregnancy.

Although insanity is determined by the social relations of man, that part of the social organization which is termed Society, and which has been developed by the idle as a diverting game, is a fertile source of nervous disease and even of insanity, affecting particularly females.  The strenuosity of the life, the nervous excitement alternating with ennui, the lack and improper times of sleep, the lack of rest and particularly of restful occupation, the not infrequent use of alcohol in injurious amounts, are all factors calculated to make a defect operative.  The so-called “coming out” of young girls is an important element in the game, and their headlong plunge into such a life at a period under any conditions full of danger to the nervous system is especially to be reprobated.  If we consider the influence of the game in other respects as conducing to lack of moral sense, to alcoholic abuse (for without the seeming stimulation, but which is really the blunting of impressions which alcohol brings, the game would not be possible), to discontent, to mental enfeeblement, it is all bad.  Curiously enough the game is one which in all periods has been played by the idle, but its evil influence is greater now than before when it was the game of royalty chiefly, because there are now more people living from the work of others.

The unusual mental action of the insane not infrequently expresses itself by suicide.  The analysis of three hundred deaths from suicide showed pathological changes in the brain in forty-three per cent, and when we think that mental disturbances are very often without recognizable anatomical changes after death, the percentage is very large.  In another analysis of one hundred and twenty-four suicides forty-four of these were mentally affected to various degrees.  Five of the men and seven women were epileptics, in ten of the families there was hysteria, twenty-four of the men and four of the women were chronic alcoholics.