74 THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 



Baer (1827), who believed that the lutein cells are derived from the connective tissue about 

 the follicle, the theca interna; and the second is that of Bischoff (1842), who concluded that 

 the cells come from the epithelial layer of the follicle, the membrana granulosa. The chief 

 arguments in favor of the first view are that, firstly, as the Graafian follicle ripens, the theca 

 cells show marked changes; they swell in volume, become rounded, and in short come to 

 resemble the lutein cell very closely (see below, p. 86, and figures 16 and 18) ; secondly, the 

 membrana granulosa of large follicles is often degenerated, and is believed to be cast off 

 at the time of rupture; thirdly, such follicles as do not rupture are filled up by proliferation 

 of the theca interna, and in this process of atresia become very much like corpora lutea. It 

 is interesting to note that the latter view happens to have for prominent defenders those 

 who have worked most carefully upon the sow's ovary, Benckiser (1884), Jankowski (1904), 

 and Clark (1898). Great doubt has been cast upon it, however, by the careful and patient 

 work of Sobotta (1896 ff.) and his followers, who maintain the origin of the lutein cells from 

 the granulosa alone, and do not admit the participation of theca cells except to form the 

 connective tissue reticulum. 



A third theory, due I believe to Schron (1863), but upheld recently by Rabl (1898), 

 Seitz (1896), Leo Loeb (1906), R. Meyer (1911), Van der Stricht (1912), and others, is that 

 both layers of the follicle form lutein cells. The upholders of this view do not deny one of 

 the arguments of their opponents, that regarding the changes of the theca interna during 

 the ripening process, but they think it is not permissible to draw conclusions from the 

 resemblances between follicular atresia and corpus luteum formation. Moreover, it is not 

 true that the granulosa is cast off from normal follicles before or at the time of rupture, as 

 is well shown in figure 1. Many of those who believe that the theca cells take part in 

 lutein-cell formation describe some of the "theca lutein cells," as they call them, remaining 

 for a time in little groups about the periphery of the corpus luteum and along the septa of 

 connective tissue which penetrate it. 



I think it may be said with fairness that most of those who have really devoted them- 

 selves to accurate studies of the corpus luteum with modern methods maintain the origin 

 of the lutein cells either from the granulosa or from both layers of the follicle. With only 

 a few specimens of very early corpora lutea at hand, I can not presume to enter this contro- 

 versy, except to mention that in the sow the granulosa undoubtedly persists after rupture 

 of the follicle, and becomes vascularized by vessels from the theca interna. After this 

 there is a gap in my series until the corpus luteum becomes solid. However, from some 

 new points in the histology of the corpus luteum, which I am about to mention, it seems 

 ! that in the sow, at least, there is a fourth possibility to be reckoned with by the investigator 

 who is to clear up this baffling question — namely, that the granulosa and perhaps part of 

 the theca enter into the formation of true lutein cells, while some of the cells of the theca 

 interna remain as distinct cells of special nature in the fully formed corpora lutea. 



It is apparent at first glance at a well-prepared section of the corpus luteum of the 

 sow that it is not the simple structure composed of a parenchyma of lutein cells and a frame- 

 work of connective tissue which is figured in the manuals of histology. The lutein cells 

 are indeed the chief element, but lying between them are other cells of at least two sorts, 

 which can be found at all stages of pregnancy. For want of better terms I shall denote 

 them as additional cells of the corpus luteum, types 1 and 2. 



Type 1 (fig. 2, b). — About the periphery of the corpus luteum, and along the septa 

 of connective tissue which penetrate it, in many sections one sees small groups of cells whicli 

 have the following characteristics: round or oval nuclei containing a moderate amount of 



