82 Proceedings of the Royal Irish Academy. 



of the cells they are only grey or yellow-brown. In PL IV, fig. 4, is a 

 »roup of luteal cells surrounding a stellate cell. The granules marked L in 

 such osmieated preparations reduce the Os04 vigorously and appear quite 

 black. There can be no doubt, from the variety of methods which show these 

 granules (they also show by iron haematoxyliu after M tiller- Formalin 

 fixation), that we are not dealing with artifacts or cell coagulates of a 

 suspicious description. 



In some parts of the sections of corpus luteum the stellate cells exhibit a 

 heavy granulation, as in PI. IV, fig. 4, even when, for some reason, the 

 granules of the luteal cells either show faintly, or are not even visible. One 

 concludes from this that the granules of the stellate cells are of a somewhat 

 different nature from those of the luteal cells, or the cytoplasm of the stellate 

 cells, being denser than that of the luteal cells, is more suitable for holding 

 the o.smic acid. In preparations made in the latter, the cytoplasm of the 

 st«llate cells is of a dense yellow colouration. 



The chemical nature of the granules within the cells of the corpus luteum 

 is not easy to ascertain. Some observers have loosely called all the blackened 

 granules of these cells neutral fat. Cell granules, which in the fresh state go 

 black in osmic acid, and reddish brown in Sudan III, are often considered 

 to be neutral fat : I have not been able to try either of these tests. The 

 osmieated tissue I examined had been previously treated in formalin : tissue 

 which has been treated in fonnalin may reduce osmic acid in almost any part 

 or in any cell organella. Nevertheless the granules which so regularly 

 blackened in formol-osmic could be extracted completely in turpentine : in 

 sections treated in turpentiue the position of the black granules is marked by 

 rows and groups of empty vacuoles. The evidence that these granules are 

 true fat is as follows : — 



Formol- Osmic. 



Blacken. 



Extract in turpentine. 



Birchromate- Osmic. 



Blacken. 



Ditto. 



Fonnol fixation alone. 



Left as vacuoles. 





The BAddence against the view that the granules are true fat is that they 

 do not occur in the same irregular manner in which true fat appears in cells ; 

 they do not vary much in indiAidual size ; they do not always reduce the osmic 

 vigorously ; and finally they correspond in position with the expected 

 arrangement of the mitochondria, i am therefore inclined to believe that 

 these granules are lipin and not true fat : this would agree with the results 

 of Cesa-Bianchi and Loisel. Phosphatides, cholesterin-fatty acid mixtures, 



