ORIGIN OF THE CORPUS LUTEUM 139 



able numbers in the early corpus luteum cells of swine (fig. 3). 

 After immersion in alcohol, xylol, ether, or other lipoid solvents, 

 both the fatty center and the phosphatid substance of the spheri- 

 cal droplet are dissolved out, leaving only a hollow sphere (ap- 

 pearing as a ring in thin sections), probably composed of proteid 

 constituents of the cytoplasm precipitated in the spherules during 

 fixation. The bodies are not seen in fresh tissues nor in material 

 fixed with very rapid coagulants like osmium tetroxide, which 

 precipitate the proteids before the oil droplets round up. The 

 microchemical evidence of these conclusions is given in the 

 articles cited. 



The appearances in question, therefore, are simply the result 

 of methods of fixation which do not preserve certain obscure 

 lipoids in* their natural diffused state. But the artifact is a 

 useful one. In the first place, it enables us to follow the changes 

 in amount of the phosphatid substance during the advance of 

 pregnancy. It also allows us to estimate the age of a corpus 

 luteum of pregnancy from the histological appearance alone, and 

 it gives us a constant (even though artificial) cytological char- 

 acteristic of the cell which can be used in determining the early 

 history of the lutein cells. Due no doubt to different physical 

 state of the cell lipoids, the phenomenon does not occur in the 

 human and bovine corpora lutea (a former statement of the 

 author to the contrary). 



THE MATURE FOLLICLE 



As the reader has perceived, one of the crucial points in this 

 debate has been as to the condition of the granulosa of the 

 mature follicle. Some investigators think that this layer de- 

 generates before rupture, others that it remains intact. It 

 would seem, offhand, an easy matter to obtain mature follicles 

 and settle the question at once. To be certain that a given 

 follicle is really mature is very difficult, however, and particu- 

 larly so in some species. Mere size is no criterion, for full-sized 

 follicles are not infrequently in a state of advanced atresia. The 

 presence of maturation processes in the ovum is no more certain 



