Chapter III. 

 The Internal Secretions of the Sexual Glands. 



The question now arises as to the nature of the mechanism 

 whereby the sexual glands exert their influence on the sexual 

 characters in different species. 



Two possibilities present themselves; an influence may be 

 by the intermediation of the nervous system (as by some kind of 

 a reflex), or directly through internal secretions which pass 

 into the circulation. Experiments with transplantation and 

 injection of sexual glands have been made on mammals, birds 

 and amphibians with the purpose of solving this question. It 

 is to-day generally agreed that the sexual glands act by means 

 of internal secretions. 



Before entering into a discussion of the experimental proofs 

 of this contention we shall state in a few words what we mean 

 by "internal secretion. "^ It is really a more or less arbitrary 

 matter to distinguish between the special internally secretory 

 organs and the other parts of the body. All organs and cells 

 in a multicellular organism are connected with and dependent 

 upon each other by the intermediation of products of metabolism 

 secreted into the body fluids. These substances may be 

 specific or otherwise for the respective organs by which they 

 are secreted. We know that the secretions produced by one set 

 of organs influence all the other cells and organs of the body. 

 Take, for instance, carbonic acid, a katabolic product secreted 

 by every cell and thus without any specifity. The action of the 

 respiratory centre in the medulla oblongata depends upon 

 the quantity of carbonic acid present in the blood. Thus 

 every cell in the multicellular organism acts by some kind 

 of "internal secretion" on the respiratory centre. This action 

 of the carbonic acid or of the hydrogen ion is a specific one. 

 The specifity of the action which different secretions have on 



* Besides the literature quoted in the text see Gley, (1914); Caullery (1913. 

 p. 115); LipschUtz (191 7). 



79 ^ 



