CHAPTER XIII. 



CAUSATION OF MENTAL DIFFEEENCE AND DISOEDEE. 



General Considerations. 



As a general rule, the causes of mental difference and dis- 

 turbance in other animals are the same in kind as, though 

 not perhaps equal in number to, those operative in man. 

 Man's peculiar, and especially artificial, habits render him 

 obnoxious to certain disturbing causes, from which most 

 other animals, living more healthy lives, are free ; while, on 

 the other hand, there are certain causes that are more power 

 fully or frequently operative in other animals than in man. 



The causes productive of insanity in the lower animals 

 are so numerous and varied that it is impossible, in the pre- 

 sent work, to do more than merely catalogue them, making 

 comments on a few of them only in order to show their 

 special power or significance. 



In man the causes of mental disease are usually divided 

 into 



1. Physical or bodily ; and 



2. Moral or mental. 



And the same classification may be convenient also in 

 regard to other animals. But in either case in the case of 

 man as much as in that of other animals such a classifica- 

 tion must be regarded as purely arbitrary, artificial, and one 

 of convenience. In the majority of cases of mental disorder 

 both in man and other animals its causes are complex or 

 mixed, partly physical or bodily, and partly moral or mental. 

 Causation is seldom simple ; the cause seldom single. Usu- 

 ally there is nothing more difficult in the study of the 

 natural history of insanity, or in the investigation of an 



