SECRETION OF THE DUCTLESS GLANDS. 893 



evidence. Total extirpation of the gland gives no decisive effect 

 upon dogs (Dandy). On guinea-pigs it is stated (Horrax) that 

 pinealectomy causes an accelerated development of the sexual 

 organs in the male. 



Organs of Reproduction. Some of the earliest work upon the 

 effect of the internal secretions of the glands was done upon the 

 reproductive glands, especially the testis,. by Brown-Sequard.* 

 According to this observer, extracts of the fresh testis when in- 

 jected under the skin or into, the blood may have a remarkable 

 influence upon the nervous system. Mental and physical vigor, 

 and the activity of the spinal centers, are greatly improved, not 

 only in cases of general prostration and neurasthenia, but also in 

 the case of the aged. It cannot be said that his assertions have 

 been corroborated by later work. Zothf and also Pregel seem to 

 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.J Making use of very young animals this observer has 

 transplanted the testes from their normal position to other regions. 

 Such annuals 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 



* "Archives de physiologic normals et pathologique," 1889-92. 

 t"Pfliiger's Archiv f. die gesammte Physiologic," 62, 335, 1896; also 69, 

 386, 1897. 



t Steinach, "Pflugef's Archiv," 144, 71, 1912. 



