ORIGIN OF THE CORPUS LUTEUM 137 



SPECIAL CYTOLOGY OF THE LUTEIN CELLS OF THE SOW 



Four years ago the writer undertook, at the suggestion of 

 Professor Mall, to study the corpus luteum at different stages of 

 pregnancy, with the aim of learning through the varying appear- 

 ances to standardize the stages as a means of determining the 

 ages of embryos and foetuses (Corner, '15). It was very good 

 fortune that led to the choice of the pig for the first studies, for 

 a useful peculiarity of cytoplasmic structure was found to occur 

 in this species. If we take a section of the corpus luteum of a 

 pregnant sow whose foetuses are perhaps 100 mm. long, fixed in 

 formol, and stain it with any strong cytoplasmic stain, study of 

 the lutein cells shows that the cytoplasm contains unstained 

 areas which are roughly concentric to the nucleus, and which 

 appear to form canal-like paths in the cell (fig. 1) . In the younger 

 corpora the canals grow more and more complex, assuming the 

 form of wide V-shaped spaces, long clefts, and circles in the 

 cytoplasm, so extensive that the nucleus is surrounded only by 

 a narrow zone of endoplasm. But it is in the corpora lutea of 

 pregnancies under 30 mm. that the highest development of the 

 exoplasmic zone is found. Here the entire outer part of the cell 

 is occupied by a curiously elaborate system of vacuoles, almost 

 every one of them in turn containing a spherule of substance 

 which, although it takes the same stain as the cytoplasm, yet has 

 a more hyaline appearance, and is seen in the section as a bright 

 ring. Within many of the spherules is found another and tiny 

 vacuole (fig. 2, r). Corpora lutea of pregnancies with foetuses 

 more than 140 mm. long contain no trace of this system (figs. 23 

 and 24), and by careful attention to the degree of its develop- 

 ment it is possible, therefore, to estimate the age of the cor- 

 responding embryo with some accuracy. Taking other histo- 

 logical features into consideration, I find myself able to detect 

 the stage of pregnancy within close limits by examination of the 

 corpus luteum alone. The same bodies are present in the corpora 

 lutea of dogs, and were seen in the lutein cells of rabbits by Cohn 

 ('03), who undertook certain microchemical studies upon their 

 nature, which I have been able to extend. It was tentatively 

 suggested, in my former paper, that they represent an elaborate 



