SECRETION OF THE DUCTLESS GLANDS. 885 



have obtained exact objective proof, by means of ergographic 

 records, of the stimulating action of the testicular extracts upon the 

 neuromuscular apparatus in man. They find that injections of 

 the testicular extracts cause not only a diminution in the muscular 

 and nervous fatigue resulting from muscular work, but also lessen 

 the subjective fatigue sensations. The natural direction in which 

 we would look for evidence of the existence of an internal secretion 

 on the part of the testes would be in their influence upon the sexual 

 characteristics and sexual appetite. Most of the recent work 

 has indicated quite clearly that the reproductive glands control 

 the development of the sexual characteristics, not by way of a 

 reflex nervous effect but by way of the blood ; that is to say, through 

 an internal secretion. This work however, tends to show that the 

 internal secretion is formed not by the reproductive elements 

 proper, the spermatozoa or the spermatogonia, but rather by the 

 so-called interstitial cells of Leydig, which lie outside of the seminal 

 tubules. When a young animal is castrated completely the sec- 

 ondary sexual characters and the sexual appetite do not develop. 

 If, however, the vas deferens is ligated, the sexual elements may 

 disappear while the interstitial cells remain and increase in num- 

 ber. In such animals the sexual instincts and characteristics 

 develop normally. The clearest proof of the importance of the 

 interstitial cells in this regard is furnished by the experiments of 

 Steinach.* Making use of very young animals this observer has 

 transplanted the testes from their normal position to other regions. 

 Such animals develop normally, show all of the usual secondary 

 sexual characteristics, and manifest full sexual desire and potency 

 at the proper period. When the transplanted glands are examined 

 it is found that the sexual elements are lacking, but the interstitial 

 cells are increased in amount. It would appear from this work 

 that sexual puberty is dependent upon the internal secretion 

 furnished by these cells, and Steinach proposes to designate them 

 collectively as the "puberty gland." This observer reports further 

 remarkable experiments in which young males (rats, guinea pigs) 

 were first castrated and then had transplanted under the skin or 

 in the peritoneal cavity the ovary from a female of the same 

 species. Und^r such conditions the graft of the ovary takes, and 

 unlike the grafted testicle both the reproductive cells and the 

 interstitial cells survive. In such animals the secondary male 

 characteristics do not develop, his genital organs remain infantile; 

 he exhibits, on the contrary, the female characteristics, as shown by 

 his size, the character of the hair, and especially by the develop- 

 ment of mammae and nipples. So far as the external charac- 

 teristics are concerned the animal is completely feminized, and 

 * Steinach, "Pfliiger's Archiv," 144, 71, 1912. 



