86 THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 



calcium. It is plain that the divergent opinions upon the question are due to incomplete 

 knowledge of the corpus luteum at all its stages. Meanwhile the clinicians are beginning 

 to put the matter up to the anatomists anew, for instance, with such statements as that of 

 Dannreuther (1914), that the dried corpus luteum of pregnancy is much more efficient 

 therapeutically than the corpus luteum of ovulation. 



I have sections of ovaries from about 25 uteri which did not contain embryos, many of 

 them having been carefully examined by another investigator who was searching for early 

 embryos. No doubt a few of them are from pregnant animals after delivery, so that the 

 corpora lutea may not all be those of ovulation. At any rate, it can be said with certainty 

 that the presence of embryos in the uterus is to be diagnosed by microscopic examination 

 of the ovary. The difference between the corpus luteum of pregnancy and that of ovulation 

 is like the difference between an army and a mob. In the corpus luteum of pregnancy there 

 is a regularity of structure which is lacking in thai of ovulation. For instance, in the latter 

 we find cells having highly developed exoplasm side by side with others having a smooth 

 undifferentiated cytoplasm and large fat-vacuoles in them (fig. 17). The fat-vacuoles 

 of the connective-tissue cells are usually much larger and more numerous than in the corpus 

 luteum of pregnancy, so that the sections are riddled with holes. It appears likely, though 

 it can not be proven, since we have no way of determining the age of a non-pregnant 

 corpus luteum from the slaughter-house, that retrogression sets in before the corpus is 

 fully formed, and affects the cells in an irregular way, so that they do not all progress through 

 the stages of their life history at one time. Whether or not there are differences of note in 

 the first 15 days I can not say, as I have no data for corpora lutea of pregnancy in the first 

 two weeks. After this period the two sorts of corpora lutea can be distinguished from 

 each other. 



INFLUENCE OF PREGNANCY ON THE STRUCTURE AND FUNCTION 

 OF THE GRAAFIAN FOLLICLES. 



It has been known for a long time that pregnancy interrupts the function of the corpus 

 luteum; that in the presence of an embryo in the uterus there is normally no ovulation 

 and therefore no formation of new corpora lutea. In animals which undergo rut or men- 

 struation these phenomena are also interrupted by pregnancy. 



To understand the causes underlying the non-occurrence of ovulation during preg- 

 nancy, we must know the life-history of the normal follicle. Fortunately this is a subject 

 upon which there is substantial agreement between all observers. As is well known, the 

 fully formed resting follicle consists of three layers: the membrana granulosa, of presumably 

 epithelial origin; the theca interna, probably of mesenchymal origin; and the theca externa, 

 of mesenchymal origin. The exact histological characteristics of the three layers vary 

 slightly in different animals, but in the pig the granulosa is composed of 3 to 10 layers of 

 rounded cells (the lowest layer, next the theca, is columnar) with round, darkly staining 

 nuclei and little cytoplasm (fig. 16, a). The theca interna is composed of 5 to 10 layers 

 of short, spindle-shaped cells, with moderate amount of cytoplasm and round, or oval, 

 nuclei, not so chromatic as those of the granulosa (fig. 16, b). The theca externa is made 

 up of definitely spindle-shaped cells of connective-tissue derived from the ovarian stroma 

 (fig. 16, e). 



Now, one of two fates awaits the unripe follicle in the course of time. It may never 

 attain ripeness, but instead may undergo degenerative changes leading to obliteration. 



