No. 2.] THE OVARIAN STROM A OF MAMMALS. 91 



I have been able to demonstrate this centrosome beyond all 

 doubt by staining with Heidenhain's iron haematoxylin and 

 then with orange G. or Bordeaux red, the best results being 

 obtained with the haematoxylin and orange G. The extraction 

 of the haematoxylin is carried just to the point where the cyto- 

 plasm has lost the last traces of the stain. Then after the con- 

 trast-stain and mounting, the haematoxylin is seen to be confined 

 to the nucleus and to a single (or double) tiny but perfectly 

 distinct granule in the center of the sphere. Error seems to 

 be impossible here because by proper extraction the centrosome 

 is the only extra-nuclear body in the cell that shows a trace of 

 haematoxylin, and in contrast to the orange about it it is per- 

 fectly sharp and well defined. Moreover, the abundance of 

 these cells and the uniformity with which the centrosome is 

 visible renders the sections most striking. The group in Fig. i 

 is drawn as seen in the section, and probably a hundred other 

 similar groups could have been selected from the same section. 

 I cannot state positively that every sphere contains a centro- 

 some, but from the very large proportion of cases that I have 

 observed it appears extremely probable that such is the case. 



It is possible to obtain fairly good preparations by staining 

 with gentian violet or with Flemming's triple stain, safranin, 

 gentian violet and orange G., but the pictures thus obtained 

 do not compare with those given by iron haematoxylin and 



orange. 



Now the question arises as to the origin of these cells and 

 their relation to the ordinary ovarian stroma. At first I 

 regarded them as belonging to the corpora lutea, but further 

 study has shown that they occupy the position, not of the cor- 

 pora lutea, but of the stroma itself. Moreover, the cells of the 

 corpora lutea are perfectly distinguishable from them. 



As stated above, the details of their origin have not yet been 

 worked out, but the following observations may throw some 

 light on the matter. 



In the ovary of the adult non-pregnant rabbit the stroma is 

 composed principally of two kinds of cells. One of these is 

 the elongated fiber cells, some of the shorter of which are 

 shown in the spindle-shaped cells with deeply staining nuclei 



