84 THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 



I have called type 2; and, most notable of all, many cells of that type which I have called 

 additional cells of the corpus luteum, type 1, which, with their nuclei, more chromatic than 

 that of the lutein cell, and their homogeneous cytoplasm, resemble the "theca lutein cells" 

 of other writers (fig. 10, b). With the increase of the connective tissue, penetrating 

 between and spacing apart the true lutein cells, these smaller, homogeneous cells are found 

 much more generally scattered through the corpus luteum than before. In osmic prepara- 

 tions they are often loaded with large densely-packed black granules (fig. 11, a). Others 

 of the interstitial cells of the corpus luteum, of all types, contain only fine, diffusely scattered 

 black granules (fig. 11, b). In the lutein cells themselves the amount of osmic-staining 

 matter is progressively lessening; the globules are found in a narrow zone at or near the 

 periphery of the cell. I think that most of the vacuoles seen at the border of the cell in 

 Mallory's material at this stage are due to the fatty substance, and that the lesser number 

 only are due to remains of the once extensive peripheral canalicular system. 



Sixth period: endoplasmic development, second part. — Pigs 170 to 220 mm. long, approxi- 

 mate duration of pregnancy 105 to 110 days (fig. 12). The diversity of staining reaction 

 is less marked than in the preceding stage, and the diversity of size of the cells is less notice- 

 able, because in the first place the lutein cells have lost the peripheral vacuolization, while, 

 secondly, the smaller interstitial cells of the corpus luteum have grown in size, and therefore 

 the two types of cells so resemble each other that it is difficult to distinguish them. Fat 

 is very slight in amount and limited to the periphery of the lutein cells, where a few granules 

 are found. The interstitial cells of the corpus luteum are often loaded with large fat globules 

 (fig. 13). 



Seventh period: beginning retrogression. — Pigs 220 to 290 mm. long, approximate dura- 

 tion of pregnancy 110 days to term (fig. 14). The only difference between this stage and 

 the preceding is that here the lutein cells frequently contain one or more fat globules larger 

 than any previously seen, which are found near the periphery of the cell, and at first in cells 

 near the periphery of the corpus luteum (figs. 14, 15). The oldest corpus luteum of my 

 series (290 mm.) contains many such vacuoles. 



THEORETICAL CONSIDERATIONS CONCERNING THE LIFE-HISTORY 

 OF THE CORPUS LUTEUM. 



I have purposely omitted theoretical discussion from the foregoing description, because 

 I do not wish false analogy or faulty deduction to belittle the value of these observations as 

 criteria for determining the age of lutein cells of pregnancy. I may be entirely wrong in 

 ascribing to the cells which I have called type 1 an independent existence and a classifica- 

 tion different from the true lutein cells, and in thinking that they resemble the theca 

 lutein cells of the descriptions of Rabl, Cohn, and R. Meyer. Those who believe that the 

 origin of the lutein cells from the theca interna alone is incontrovertibly established will 

 simply say that, as all the cells of the corpus luteum arise from one source, what I have 

 described are merely stages or variants of one type of cell. On the other hand, those who 

 adhere to the now widely accepted view that both layers of the follicle enter into the forma- 

 tion of the lutein cells should see no difficulty in my tentative proposition that, in the sow 

 at least, the theca cells perhaps persist partly as distinct cells throughout pregnancy. 

 For, as I have mentioned, Rabl, Cohn, and R. Meyer have thought them to persist well 

 into pregnancy, and Van der Stricht indeed thinks that they persist throughout pregnancy 

 as cells of internal secretion, perhaps less active than the true lutein cells. 



