ORIGIN OF THE CORPUS LUTEUI^ 177 



beside the endothelial cells of the capillary wall, except here and 

 there along the greater vessels which run in from the periphery. 

 Since there are multitudinous fibrils, and no 'fibroblasts' to pro- 

 duce them, one is forced to suspect that, as in the liver, the 

 endothelial cells themselves lay down the reticular fibrils. This 

 evidence by elimination would appear to be supported by 

 observation of the actual fact, but the question needs fuller 

 investigation/ 1 



Whatever be their source, the amount and density of the reticu- 

 lar fibrils of the corpus luteum increases steadily from the na- 

 tivity of the organ until retrogression, when the organ is entirely 

 replaced by scar tissue (fig. 26). It is along the large septa 

 that the fibers first become dense, perhaps because a few con- 

 nective-tissue cells of the theca externa are often drawn into the 

 folds produced by the collapse following follicular rupture. 



RETROGRESSION OF THE CORPUS LUTEUM 



Owing to conditions of the meat-packing trade, it is difficult to 

 obtain ovaries of sows within a few days after parturition. 

 Study of the two specimens from the seventh and tenth days after 

 littering shows that regression of the corpus luteum is as rapid as 

 its appearance. By the seventh day the structure, which was 

 a flesh-colored body 10 or 11 mm. in diameter before parturition, 

 is only half this size; it has already shrunken until it is almost 

 buried in the ovarian stroma, and it has acquired a yellow-brown 

 color. By the time another ovulation occurs, the former corpora 

 lutea are dense scar-like nodules of connective tissue rendered a 

 pale yellowish brown by the presence of pigment in the shrunken 

 cells caught in the meshes of the scar. The microscopic changes 

 during this process are obscure to me for lack of material, and 



3 The resuRs of a study of the question made since the completion of this 

 paper have proved that our hypothesis was correct, and that in the corpus luteum 

 and a number of other organs part or all of the reticular framework is laid down 

 by the cells of the capillary endothelium. (See a contribution by the author to 

 the forthcoming volume in memory of Dr. F. P. Mall in the Publications of the 

 Carnegie Institute of Washington, no. 272.) 



