150 INTERNAL SECRETIONS 



very different in each case. But the differences seen are 

 possibly caused by other factors interfering with the backward 

 development (1921 c). 



Wholly different from the behaviour of the tubules is that of 

 the interstitial tissue. In the normal testicle of the mouse or 

 the rat (Fig. yy) we find between the seminiferous tubules a fine 

 net of connective tissue, and between the fibres of the^latter 

 here and there single cells of Leydig or httle nests of these cells. 

 In the transplanted testicle the number of the cells of Leydig is 

 enormously increased (Figs. 76 and yy). The cells of Leydig 

 now form a compact mass of thick cords situated between the 

 degenerate seminiferous tubules. The network of connective 

 tissue fibres between the proliferated interstitial cells is very 

 insignificant. It seems that the number of the interstitial 

 cells in the transplanted testicle is several times greater than 

 in the normal one. It was objected that there is no real 

 increase of interstitial tissue between degenerating tubules, 

 the increase being only an apparent one. This may be true 

 in some cases. But various observations certainly show that 

 this objection is not always justified. From our own experi- 

 ments I reaHsed that it is not difiicult to determine whether 

 the hj^ertrophy of the interstitial tissue is real or only apparent. 

 And in our experiments with partial castration there was often 

 an enormous hypertrophy of the interstitial cells in small 

 fragments of the upper pole of the testicle (Figs. yS and 79). 

 It would be out of place to discuss this question more fully here. 

 My paper (1923) may be referred to. 



As the animals with an engrafted testicle reached full 

 maturity, although the seminiferous part of the graft ceased 

 to develop further, or else degenerated, we must conclude that 

 the internal secretion of the sexual gland does not depend on 

 the accomplishment of spermatogenesis or upon the presence 

 of spermatozoa. Full sexual maturity is possible without any 

 spermatoza in the graft. According to Steinach, the graft does 

 not remain always in the same condition. A few months after 

 the transplantation the cells of Sertoli also undergo a degenera- 

 tion, and according to Sand this may occur very early. The 

 seminiferous tubules lose their structure and disappear; the 

 testicle now consists almost entirely of interstitial cells repre- 

 senting, according to Steinach, an "isolated puberty gland." 

 I made a similar observation in our experiments with partial 



