SELF-PRESERVATION AND THE MENTAL LIFE 155 



infection may so poison the nervous system, in an 

 insidious way, that a powerful mental shock, in itself 

 insufficient to overcome the nervous stability, now 

 suffices to break the equilibrium which has been 

 before maintained with slender margin. Or the use 

 of alcoholic drinks may have paved the way so effec- 

 tively that a relatively mild illness from typhoid 

 fever or pneumonia finds the nervous mechanism 

 uncommonly vulnerable to toxins which would 

 ordinarily have been prevented from precipitating 

 the disorder of personality or the severe nervous 

 disorder. Instances of such duplex causation might 

 be multiplied, and even more complex instances of 

 causative action could be pictured. What has been 

 said must suffice to illustrate the principle at issue. 

 That erroneous habits of life play an enormous 

 part in creating weaknesses is an incontrovertible 

 commonplace, but, nevertheless, one that is too little 

 heeded. Faulty life habits operate through the life 

 channels that have been already described, through 

 the creation of foci of irritation in the sensory paths 

 and through encouraging the access of poisonous 

 materials to the cerebral centers. It is worth while 

 to give a list of the more important faulty life habits 

 and then to give some examples of the way in which 

 they lead to the disturbance of cerebral function. 

 It is a short and prosaic list made up of the following 

 items : the improper and excessive use of food, in- 

 cluding the abuse of alcohol, tea, and coffee ; the over- 

 frequent repetition of sexual excitement ; the exces- 



