Chapter IV. 



The Seat of Production of the Internal 

 Secretion of the Testicle. 



From the facts communicated in Chapter III. it follows that 

 in all vertebrates and in some invertebrates the sexual glands 

 influence by an internal secretion the sexual characters both 

 in forming and also in conserving them. There are different 

 tissues in the sexual glands, and the question now arises which 

 of these tissues represent the organ of internal secretion in the 

 sexual gland. The question is, indeed, as Gley (1922) has 

 rightly pointed out, histological rather than physiological. 

 But it is one which can be decided only b}^ the help of 

 experimental physiology. 



At first sight one might suppose that the internal secretion 

 of the testicle is produced by the generative part. This sugges- 

 tion has been contested in recent years by several authors. 

 A long series of investigations has encouraged the belief that 

 the internal secretion ascribed to the sexual glands is elaborated 

 by the so-called cells of Leydig, the "interstitial substance," 

 or "interstitial cells," situated in the connective tissue between 

 the seminiferous tubules. It was shown by these investiga- 

 tions that the formation and the preservation of the sexual 

 characters in the organism of mammals occur also when the 

 generative part of the testicle is in a state of degeneration. 

 Bouin and Ancel (1903) were the first to identify the cells of 

 Leydig with the organ of internal secretion in the mammalian 

 testicle. They called these cells Glande inter stitielle, or inter- 

 stitial gland, whereas Steinach (1912) described them later 

 under the name Puberty gland. 



As regards other vertebrates and invertebrates no sufficient 

 knowledge of the interstitial cells in the testicle yet existed for 

 locating the internally secreting elements. Not until lately 

 has a systematic investigation in this direction been under- 

 taken for amphibians and birds and fishes, but this has now 

 been done by Bouin and his co-workers. 



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