CHAPTEE XYIII. 



MIXED CAUSES OF MENTAL DIFFERENCE AND DISORDER. 



THERE are obviously certain causes of mental disturbance in 

 the lower animals which are of a very mixed character, and 

 cannot appropriately be classified under either e physical ' or 

 c moral.' Belonging to this mixed or composite category, 

 possessing characters that are partly physical, partly moral, 

 may be conveniently ranged 



I. Heredity and predisposition, including temperament, 

 diathesis, and idiosyncrasy. 



II. Artificial life ; which involves 



Captivity. 

 Monotony. 

 Inactivity. 

 Solitude. 



Repression or non-gratification of the most impe- 

 rious of the bodily instincts. 



III. Privation, involving 



Starvation. 



Homelessness. 



Exposure. 



IV. Man's cruelty, neglect, or injudicious treatment. 



It is impossible to exaggerate, either in man or other 

 animals, in the etiology of insanity, the importance of that 

 combination of conditions known as predisposition. These 

 conditions may represent in a single individual a whole 

 series of bad ancestral influences. 



Heredity is as powerfully operative in other animals as 

 in man ; so that insanity and eccentricity ; the nervous or 

 insane neurosis, diathesis, psychosis or temperament ; a con- 



