INTERNAL SECRETION OF TESTICLE 155 



in a preceding section that in the experiments where cells of 

 Sertoli and spermatogonia were present in the tubules eunu- 

 choidism occurred when interstitial cells were underdeveloped. 

 In view of these considerations the criticism directed against 

 the evidence provided by the X-ray experiments in support 

 of the theory of the interstitial cells is deprived of its importance. 

 Thorek (1923) has made testicular homoiotransplantation in 

 apes (Cynocephalus and Macacus) one to two years after castra- 

 tion ; immediately following this implantation, the animals were 

 subjected to the action of X-rays. Removal of specimens 

 proved that generative tissue was absent. Nevertheless, out 

 of five animals four revealed a return of sexual potency. 



6. The Relation between the Quantity of Interstitial 

 Tissue and the Hormonic Effect. 



(a) Is there a compensatory hypertrophy in the testicle ? 



We have seen that the number of interstitial cells may be 

 greatly increased under certain conditions. It may be, as 

 already pointed out, that in some cases with retained testicles, 

 ligature or irradiation, this increase is only an apparent one. 

 But no doubt in certain of Steinach's transplantation experi- 

 ments, and in many of our own with partial castration, the 

 hypertrophy of the interstitial tissue was very great {Figs. 

 y^ to 81). 



We do not know the real cause of this hypertrophy. It seems 

 that it always occurs when a degeneration or a retrograde 

 development of the tubules takes place. My observations 

 agree with Kyrles (1911) in regard to the hypertrophy of the 

 interstitial cells which often occurs in the same testicle or 

 testicular fragment in the neighbourhood of the degenerated 

 tubules only, and not in that of the normal ones. This is an 

 indication that the cause of this hypertrophy is often local rather 

 than general. Further, I observed an enormous hypertrophy of 

 the interstitial cells in a small testicular fragment {Fig. 82) in a 

 guinea pig, notwithstanding that the second testicle was present 

 (1922 c, f). There was an hypertrophy of interstitial cells also 

 in those experiments in which both testicles were transformed 

 into upper fragments without reducing the total testicular mass 

 {Fig. 83). From these observations one must conclude that 

 the hypertrophy of the interstitial cells occurring in small 



