144 CAEL E. MOOEE 



ova have been studied and the steps in this degeneration form a 

 perfectly distinct graded series in its atypical progression. 

 Figure 2 (a section of a four and a half months' graft from male 

 51 E) indicates very well the relative number of atretic and 

 normal follicles present in one section of some of these grafts; 

 follicles a and b are normal. 



The normal ovary, however, consists not alone of follicles 

 (stratum granulosum, ovum, internal and external thecal layers), 

 but also situated between the follicles and in the midst of the 

 connective-tissue stroma are cells larger than connective-tissue 

 cells, possessing well-stained nuclei and a reticular-like cytoplasm 

 in ordinary stained preparations. Fixed with a solution con- 

 taining osmic acid, however, these cells — singly or in groups — 

 are very distinct; they reduce osmic acid and, if mounted un- 

 stained after such a fixation, they stand out as masses of black- 

 ened cells in contrast to the follicles and connective tissue of 

 the ovary, both of which are but faintly seen. Such cells are 

 usually spoken of as 'lipoid containing cells' and they constitute 

 what are ordinarily called interstitial cells. 



The question of the interstitial cells of the ovary is one con- 

 cerning which few definite conclusions can be drawn. The 

 literature is an enormous one and in so far as the theoretical 

 considerations are beyond the scope of this paper a review of this 

 literature will not be attempted.^ But in so far as reference 

 must be made to the interstitial cells of these grafts, the writer 

 wishes to define his position in reference to this matter. The 

 term 'interstitial cells' will be applied, in the case of the ovary, to 

 those cells of relatively large size, situated between the follicles, 

 in the connective-tissue stroma, whose nuclei are well stained, 

 cytoplasm of reticular character, and which blacken after fixation 

 with osmic-acid preparations. Figures 9 and 10, small sections 

 of a normal rat ovary thirty-fsix days after birth (fixed in strong 

 Flemming's solution and mounted unstained), portray the 

 characteristic masses of these cells; the lipoid-laden cells of the 

 theca interna are also plainly visible. And at least one origin 



8 For a review of the literature on interstitial cells the reader is referred to the 

 papers of Kingsbury and Rasmussen. 



