THE CAUSES OF INSANITY 473 



renders him incapable of being so affected by the environment as 

 to learn from it. 



774. But in another sense the environment through violence, 

 disease, alcoholism, business worries, religious and sexual excite- 

 ment, and the like may act directly as a cause of insanity by 

 injuring the brain of the sufferer, or by injuring the germ-plasm 

 contained in his germ-cells. That is to say, it may cause 

 immediate insanity, or be a cause of a tendency to insanity in 

 descendants. Cases of insanity, especially of lunacy which is a 

 disease of adult life, plainly traceable to injury or disease sustained 

 by the sufferer himself, are not uncommon. We need not dwell 

 on such instances, the causation being obvious ; the difficulty lies, 

 not in perceiving the right means of prevention, but in applying 

 them. Our interest centres in those more obscure cases in which 

 the individual is born insane (i.e. more or less incapable of learn- 

 ing), or born predisposed to become insane (i.e. to become a 

 lunatic.) Such cases are due either to injury sustained by the 

 germ-plasm, or to spontaneous variation. 



775. Probably injury to the brain occurring during intra-uterine 

 life (especially from maternal disease or alcoholism) accounts for 

 some cases of filial insanity. Probably, however, such injury is 

 much more frequently a cause of death occurring before birth or 

 shortly afterwards. It may be that the high infantile mortality 

 of urban as compared to rural areas is due in a measure to this 

 cause. 1 Cerebral injuries, whether acquired before or after birth, 

 are not transmissible. But germinal defects tend to be inherited. 

 If the variations which result in insanity are usually spontaneous, it 

 is beyond our power to diminish their frequency. We can only, 

 by controlling the output of offspring by the * innately ' insane, 

 prevent their perpetuation in descendants. If, on the other hand, 

 they are usually caused (on the occasion of their first appearance 

 in a line of descent) by the direct action of the environment on 

 the germ-plasm, it may be within our power, not only to prevent 

 their perpetuation, but also, by improving the environment, their 

 initial occurrence. 



776. But every argument which tells against the hypothesis 

 that variations in general are due to the direct action of the 

 environment tells equally against the hypothesis that those 



1 " It is not necessary to dwell upon some other causes of mental defect, such 

 as disease or accident in early life, or even before or at birth, operating through 

 injury to the brain. Cases of this kind are recognized by all ; and do not com- 

 plicate the present question. They occur in comparatively few instances (op. cit., 

 vol. viii. p. 185). 



