98 Discussion 



believe that these cells are transitional forms between fibroblasts and 

 mature Leydig cells. In the course of this study, therefore, I have 

 become more receptive to the suggestion that has often been made in 

 the literature to the effect that fibroblasts or fibroblast-like cells are 

 transformed into Leydig cells during adult life. 



Zuckerman: Would it be possible to arrange any experimental con- 

 ditions in which the relative frequency of the transition from one to the 

 other type of interstitial cell could be studied ? I recall that when most 

 cells which could possibly be spermatogonia disappear from the semini- 

 ferous tubule, and the cells of Sertoli become denned with considerable 

 clarity, one occasionally finds that the interstitial cells swell. 



Fawcett: It might be possible to study this, but even if one could set 

 up experimental conditions that would change the relative frequency of 

 the interstitial cell types, it would be difficult to make statistically valid 

 observations on this with the electron microscope, because one's field 

 of view is so restricted and the sampling of the cell population so small 

 that I believe the experimentally produced shifts would have to be very 

 great to be detected at all. 



Wislocki: With reference to the interstitial tissue, I recall that it 

 varies considerably — histologically — in different mammals. It would 

 be interesting to examine different types of interstitial tissue with the 

 electron microscope. I recall that in rodents, for example in mice and 

 rats, that the cells are more fusiform or spindle-shaped with fewer 

 epitheloid cells of the Leydig type than one sees in man, or, to cite 

 another example, in the testes of deer. Thus there is a range to be 

 explored with reference to various cytological types. 



I presume that you believe that the ketosteroids of the male gonad 

 are secreted by the Leydig cells. In that event, would you equate the 

 lipid droplets or any other organelles which you have seen in these cells 

 with the production and storage of ketosteroids ? 



Fawcett: I presume that the ketosteroids are present principally in the 

 Leydig cells, and their solubilities are such that it is most likely that 

 they are in the lipid droplets that are preserved with osmic acid. As 

 you know, lipid is not nearly as abundant in human interstitial tissue 

 as it is in the cat. All of the slides of interstitial cells that I have pre- 

 sented have been from the human testis. The greater amount of lipid 

 in the cat testis made it technically more difficult to study. 



Adjacent Leydig cells may differ greatly in the abundance of the 

 minute vesicular component of their cytoplasm. We have wondered if 

 this variation reflected a difference in their secretory activity, but what- 

 ever the content of these vesicles may be, it is not preserved by osmium 

 fixation and probably is not a steroid containing secretory material. 



Wislocki : Pollock, a pupil of Stanley Bennett, working in my depart- 

 ment (Pollock, W. F. (1942). Anat. Rec, 84, 23) described the inter- 

 stitial cells of the cat's testes as containing cytoplasmic material which 

 gave a positive phenylhydrazine reaction and birefringent crystals 

 which were increased by treatment of the tissue with digitonin. It was 

 concluded that these reactions, plus certain solubility properties, indi- 

 cated the presence of steroid compounds in the cells. I wonder whether 



