THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 89 



ference the wall presents, as would be expected, the structure of a normal unripe follicle. 

 At one point, however (fig. 21, a), for a space of 3 mm. the whole theca interna is doubled 

 or tripled in thickness, its cells show the appearance of ripeness, and have begun to invade 

 the granulosa (fig. 22, a). The granulosa cells, in turn, are 20 to 30 microns in diameter 

 and many of them have vesicular nuclei with prominent nucleoli; they are filled with fat- 

 vacuoles, and some of them have in their cytoplasm the ring-formations of young lutein 

 cells. In short, the granulosa cells are turning into lutein cells (fig. 23). 



Seitz (1905) has emphasized the transformation of theca-interna cells of atretic follicles 

 into lutein-like cells as a physiological phenomenon in pregnancy. While I do not consider 

 this process as uniformly present in the sow, as Seitz maintains it is in the human, still we 

 do occasionally find follicles lacking the granulosa, but with the theca interna cells full of 

 fat-vacuoles and enlarged just as in ripe follicles. It is hard to see how it is to be decided 

 whether these were normal ripe follicles at the beginning of pregnancy, which are merely 

 becoming atretic, or whether they were formerly atretic follicles in which the formation 

 of theca-lutein cells is taking place, as Seitz would have it. 



Here we come to the border-line between normal and pathological anatomy of the 

 ovary. While my specimens of ovarian cysts were not collected with a view to formal 

 study, still I shall risk presenting a few incidental observations in the hope of calling atten- 

 tion to the unusually promising opportunity offered by the sow's ovary for the study of the 

 pathology of the Graafian follicle and the corpus luteum. Cysts are extremely common, 

 are often multiple, and are frequently found in ovaries containing normal corpora lutea 

 of ovulation, so that comparisons can be made. It needs only time and patience to collect 

 a great number, and the result would undoubtedly give us explanations of much that is 

 obscure concerning these tumors. 



In glancing over the 13 specimens of ovarian cysts lined by lutein cells which I have 

 collected, it at once appears that they fall into two classes. First, there are cases in which 

 one of a crop of corpora has merely retained its original cavity beyond the normal time, the 

 cavity has become fixed, and may have become much enlarged. Second, there are cystic 

 cavities in the ovary which are lined by lutein cells, but which we can not as surely say came 

 from the corpora lutea, as they may merely represent atretic follicles in which lutein-cell 

 formation has taken place. One's view of the origin of these cells will depend entirely 

 upon the view of the origin of the lutein cells of normal corpora. As will have been gleaned 

 from this paper, the writer has tentatively come to the belief that the true lutein cells are 

 derived from the granulosa cells, but that the theca interna gives rise to cells resembling 

 lutein cells, which seem in part to remain as special cells in the fully formed corpus luteum, 

 but most of which are lost, either by reverting to connective-tissue cells of the ordinary 

 kind or by becoming themselves genuine lutein cells. On this theory, we should have the 

 following kinds of lutein-cell cysts: 



I. Arising in corpora lutea which have remained cystic or have undergone cystic degeneration. 

 II. Arising in follicles: 



a. Accessory lutein-cell formation from both layers of normal follicles, as described by 



Meyer. 



b. Accessory lutein-cell formation from the theca alone, as in atretic follicles. 



It is of clinical importance to know something about the life-history of lutein-cell 

 cysts— for instance, whether such a cyst may persist and by its activity inhibit ovulation, 

 as in certain women, in whom persistent corpora lutea seem to cause sterility. Now, the 



