126 INTERNAL SECRETIONS 



mentioned, the number of interstitial cells is increased, they 

 are of the same type as in the foetus. Later on a pigmentation 

 of the interstitial cells takes place; this seems to begin at 

 about 21, and increases with age. In old age the pigmentation 

 is especially remarkable. The pigmentation is a brownish- 

 yellow one. Kasai speaks of the pigmentation as due to 

 atrophy because the pigment is absent in those cells which 

 have just divided. But it must be said that the question as 

 to whether the number of interstitial cells in the testicle in- 

 creases by division, is not yet decided. It is probable, however, 

 that, in general, increase of interstitial tissue implies trans- 

 formation of quiescent cells, which are more or less like common 

 connective tissue cells, into true interstitial cells. There has 

 been much discussion as to whether mitosis occurs in inter- 

 stitial cells. Although we observed numerous testicles of 

 different mammals in our Institute, Wagner only twice found 

 mitosis, both times under experimental conditions (Fig. 66). 

 The transformation of the quiescent cell into a true interstitial 

 one is characterised, as already said, by changes in the nucleus ; 

 the spherical nucleus of the embryonic interstitial cells becomes 

 elliptic later, and at puberty the nucleus becomes again 

 spherical and maintains this shape. 



In considering all the changes the interstitial tissue under- 

 goes throughout life from the foetal condition till old age, w^e 

 see that there are evidently two summits or climaxes in the 

 development of the interstitial cells: the first being in man 

 at about the fourth foetal month, the second at the time of 

 puberty. As we have seen above the same seems to be true for 

 other mammals, and it may be that this is the general nile for 

 all mammals, as Aron has pointed out. We shall see how this 

 may be understood from a functional point of view. The 

 histological side of the question, however, needs still further 

 thorough investigation, especially in man. 



Attempts have been made to prove that the interstitial cells 

 can perform the endocrine function of the sexual gland in 

 mammals, especially by experimental destruction of the 

 generative part of the testicle. But in all these experiments 

 the interstitial tissue in reahty has not been isolated, as the 

 cells of Sertoli and possibly also the generative cells at 

 certain stages generally survive. Attempts based upon clinical 

 observations also have been made to establish the theory 



