NERVOUS SYSTEM AND HEREDITY 207 



mental diseases are hereditary harmonise with this 

 view? It is, perhaps, not impossible that those men- 

 tal diseases that are hereditary are, in reality, chem- 

 ical diseases caused by poisons that are formed in the 

 body just as special substances, for instance, alcohol, 

 hashish, and other intoxicating substances, produce 

 temporary mental diseases (3). The delirium of fever 

 as well as certain other mental diseases may owe their 

 origin to poisons which are formed in the body. It 

 is quite possible that these poisons are also formed 

 in the normal body. It is only necessary that they be 

 formed in somewhat larger quantities or destroyed 

 in somewhat smaller quantities in the body of the in- 

 sane than in the normal man. It is further not at all 

 necessary that these hypothetical poisons which cause 

 mental diseases be formed in the central nervous sys- 

 tem. They may be formed in any organ of the body. 

 It is only necessary that they affect the central nervous 

 system - - in other words, that they be nerve-poisons. 

 Nothing is better qualified to make this view clear 

 than the result which the destruction of the thyroid 

 gland has on the mental and physical development of 

 children. We know that in case of degeneration of the 

 thyroid gland the growth and mental development of 

 children are retarded. Idiocy may result from the de- 

 struction of the thyroid gland. It has been found 

 that an improvement or even a cure can be attained 

 by feeding patients afflicted with this trouble with 

 the thyroid substance of animals. Baumann found 

 that the thyroid gland contains an element which is 



