24 'CAKEY P. McCOKD 



control cock. /The difference begins to manifest itself five months after 

 the operation and increases constantly up to the ninth month. The opera- 

 tion produces no effect on the general development of the body in the fowl. 



"The extirpation of the pineal gland, in the very young rat, produces 

 no appreciable effect in the female ; in the male it provokes a more rapid 

 somatic development and the maximum difference is observed, between 

 the weight of the operated animals and the controls, twenty-six to thirty 

 days after the operation. Then the weight of the experimental animal 

 gradually becomes equal to that of the control. 



"At the moment when the difference in weight reaches the maximum, 

 one observes also a markedly greater development of the testes in the ex- 

 perimental animal. The difference in the testes disappears when the 

 weight of the body becomes equal. 



"The histologic examination of the testes, in the cock as well as in the 

 rat, at the time of maximum difference in volume, reveals a uniform de- 

 velopment very advanced in all of the tissues of the gland ; the diameter 

 of the canaliculus is increased, the opening enlarged ; the mass of sper- 

 matozoa which fills the canalicular opening is greater; the canaliculi are 

 more separated from each other and, consequently, the interstitial tissue 

 shows greater development. There is no difference in the spermatogenetic 

 process, if one cxcepts the quantity of spermatozoa which fills the larger 

 opening of the canaliculus. 



"The canalicular tissue and the interstitial cells being uniformly more 

 developed in the experimental animal, it is impossible to say that to any 

 of these tissues is due the greater development of the secondary sexual 

 character in the cock and the somatic development in the rat, 



"The experiments on the rats have shown that the extirpation of the 

 pineal gland does not determine an absolute hypertrophy of the testes, 

 but a premature development of them. Forty-eight days after the opera- 

 tion, the operated rat cannot be distinguished from the control. This 

 observation confirms the theory which attributes to the pineal gland an 

 inhibiting function in the sexual development ; we learn from this that 

 with the beginning of puberty there coincides an involution of the pineal 

 gland." 



Biedl's Experiments. Biedl stated in 1913 in regard to his work in 

 removal of the pineal gland : "I have occupied myself for some time 

 with experiments, the main object of which has been to determine the 

 clinical results of pineal suppression. I have succeeded, so far, in ex- 

 tirpating the pineal gland by a method similar to that which I employed 

 in hypophysectomy. As far as my observations go, the pineal gland in 

 the adult animal is a negligible quantity; my experiments with young 

 animals are not as yet complete." 



Horrax Experiments. Horrax in 1916 reported the successful re- 

 moval of the pineal from guinea pigs and rats. The guinea pigs when 



