SELF-PRESERVATION AND THE MENTAL LIFE 153 



mechanisms that habitually hold in check the emo- 

 tions, or may even account for irritative discharges 

 of nervous energy from the special sensory centers 

 of the brain. In the former case, there may arise 

 emotional outbreaks constituting irregular con- 

 duct ; hi the latter case, there may be hallucinatory 

 excitement which, if uncorrected by the force of 

 logical intellectual processes, may lead to irrational 

 thought, speech, and action. And it is true that the 

 abnormal sensory stimulation which shows itself in 

 such mental aberrations may rise into conscious- 

 ness with hardly enough definition to enable the 

 subject to take cognizance of it as a distinct disturb- 

 ance. An impaired tooth, an ulcer of the stomach 

 or colon, a displaced uterus, an enlarged prostate 

 gland, may each furnish sensory stimuli capable of 

 inducing, directly or indirectly, disorders of a mental 

 nature in persons whose nervous systems are sensi- 

 tized by other injurious agencies, or by inherent 

 organization, so as to give them the vulnerable 

 quality of instability. 



Medical science has still much to acquire in knowl- 

 edge of the causative processes that lead to those 

 disturbances of functional balance in the cerebrum 

 which constitute nervous and mental disorders, 

 and it is far from the purpose of this essay to attempt 

 to point out these needs in detail or to supply them. 

 Nevertheless, no intelligent discussion is possible of 

 the self-preservative instinct which so largely molds 

 human personality without taking account of the 



