EXTERNAL INFLUENCES AS CAUSES OF VARIATION 269 



Specific secretions and glandular activity. The fact just men- 

 tioned introduces a subject full of interest. It appears that each 

 species, and perhaps each individual, is engaged in the produc- 

 tion of chemical substances (whether the result of anabolic or 

 katabolic activity is uncertain) which exert specific action upon 

 living matter. 



It is significant that some of the lower organisms producing 

 definite substances die from the injurious effects of their own 

 product, 1 unless this is removed as formed, and that higher ani- 

 mals are supplied with elaborate excreting apparatus, strongly 

 suggesting that certain of their products are deleterious to the 

 organisms that produced them, while in other cases they are 

 clearly beneficial. In this connection Loeb remarks : 2 



It is perhaps not impossible that those mental diseases that are heredi- 

 tary are, in reality, chemical 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. 

 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 some- 

 what smaller quantities in the body of the insane than in the normal man. 3 



It is further not at all necessary that the hypothetical poisons which 

 cause mental diseases be formed in the central nervous system. 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 devel- 

 opment of children. We know that in case of degeneration of the thyroid 

 gland the growth and mental development of the child are retarded. Idiocy 

 may result from the destruction 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. 4 Baumann 

 found that the thyroid gland contains an element which is contained in no 

 other organ of the body, namely, iodin. 



1 The yeast plant that forms alcohol dies when the solution has reached a 

 strength of about 20 per cent. 



2 Loeb, Physiology of the Brain, p. 207. 



3 It is said by Lombroso, and others agree, that the criminal is characterized 

 by excessive amounts of urea. 



* Medicinal preparations from various glands are now regularly supplied by 

 the large slaughterhouses, 



