SO GLANDS IN HEALTH AND DISEASE 



"coming on of heat" or "rut" in animals seems to 

 be related to menstruation in human females. Now 

 it is a remarkable fact that this "rut" is no longer 

 noticed upon the extirpation of the ovary, but is 

 again brought on by the transplantation to another 

 part of the body of the ovary belonging to a similar 

 animal. From what has already been said on the 

 subject of transplantation, it must be perfectly evi- 

 dent that an experiment of this kind admits of but 

 one conclusion : that the nervous mechanism plays 

 but a secondary part, if it plays a part at all ; but 

 that on the other hand, the ovary must discharge 

 into the blood some substance or substances which 

 give rise to the phenomenon in question. This, of 

 course, means that the ovary, in addition to giving 

 rise to an external secretion in the form of ova, 

 that contributes to the reproduction of the species, 

 must be the seat of an internal secretion. 



We now know that the two types of secretion are 

 produced by two different types of cells. The in- 

 ternal secretion is developed by the so-called "in- 

 terstitial cells," the name of which has become fa- 

 miliar to the lay reader ever since topics on reju- 

 venation have become popular with newspaper 

 editors. These cells lie altogether outside of the 

 tubes that are responsible for the flow of the ex- 

 ternal secretion. It is, in fact, possible to tie the 

 tube that, in the male, connects the testes with the 

 ejaculatory tube (the "vas deferens"), thereby 



