80 THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 



(3) The fat content changes, at first decreasing. In the cells of the type most abun- 

 dant at the middle of pregnancy, in which the endoplasmic zone occupies half or more of the 

 cytoplasmic area, the globules of osmic-blackening material are found in amount much less 

 than at previous stages, and clustered at the margin between exoplasm and endoplasm. 

 Toward the end of pregnancy, when the fetuses are 200 mm. or more in length, the lipoid 

 material has practically disappeared from the cell, being found, if present, as a few globules 

 at the periphery. But still later, in the corpora lutea of pregnancies of 270 mm. or longer, 

 many cells contain one or two globules twice as large as those previously seen, and which 

 are often observed in ordinary sections as large vacuoles, sometimes as large as the nucleus, 

 in the cytoplasm. This later deposition of fat I take to be a sign of senility of the tissue, 

 whereas the large amount of lipoid in the early lutein cell would seem to be correlated with 

 physiological activity. I have already mentioned the similar conclusion of Van der Stricht 

 regarding the corpora lutea of the bat. It is very interesting to note that the occurrence 

 of fatty substances in the connective-tissue cells and in those cells which I have called type 1 

 is in inverse ratio to that of the lutein cells. At 20 mm. only relatively few and very small 

 osmic-blackening granules are found in the spindle cells, but as pregnancy advances fat is 

 deposited in larger and larger masses until at 250 mm. the nuclei of nearly all the interstitial 

 connective- tissue cells are hidden by the large, closely packed fat globules. 



(4) Another change with advancing age of the fetuses is in the chromatic granules of 

 the endoplasm, which appear to grow larger and more apparent, reaching sometimes a 

 diameter of 2 microns. 



Throughout all this change the size of the lutein cell remains practically the same. 



PREVIOUS OBSERVERS ON THE CORPUS LUTEUM AT VARIOUS STAGES OF PREGNANCY. 



While it has been recognized in a vague way by some authors that the corpus luteum 

 is not the same at all stages of pregnancy, others hold that after the organ is formed it 

 maintains its structure in the same state until delivery or at least until retrogression sets in, 

 as, for instance, Ravano (1907) and R. Meyer (1911). At any rate, the attempt has never 

 been made to trace the changes carefully and to relate the corpus to the stage of the fetus at 

 all times of pregnancy. In general, investigators have recognized merely three stages of 

 the corpus luteum, namely formation, maturity, and retrogression. Robert Meyer would 

 divide the first stage into two, proliferation and vascularization. Cesa-Bianchi, on the basis 

 of his work on the evidences of internal secretion in the corpus luteum of swine, mares, and 

 cows, mentioned above (1908), finds three stages of the lutein cells. In the first or prepara- 

 tory period, the lutein cells are of relatively small dimensions (15 to 20 microns), with clear 

 and regular contour, round or oval form, nucleus almost central, with rich chromatic net 

 and marked nucleolus, protoplasm homogeneous or uniformly granular, not presenting 

 granules, vacuoles, or inclusions. This description does not fit the stage of formation as I 

 find it in the sow, but it is not easy to say at what time of pregnancy Cesa-Bianchi places 

 his first stage, as he does not give full measurements. His second period is characterized 

 by the presence of abundant granulations in the cytoplasm. The lutein cells are 30 to 40 

 microns in diameter; in form they are irregularly polyhedral, with excentric nuclei which 

 are vesicular, poor in chromatin, and possess numerous nucleoli. The cytoplasm presents 

 two zones: the endoplasm, directly encircling the nucleus and filled with the chromatic 

 granules described by him; and the exoplasm, presenting vacuoles of varying size. The 

 third period is characterized by the presence in the cytoplasm of numerous drops of fat. 



