90 THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 



lutein cells in cystic tumors are not often as well preserved as in normal tissue, but I believe 

 that in all the specimens in hand the lutein cells are of the same age as those of the normal cor- 

 pora in the same ovary. I have not seen lutein-cell cysts containing active-looking cells 

 of different age from the corpora lutea present. Presumably, then, the lutein cells of cysts 

 are as transient as normal lutein cells, and in cases where the cystic formation persists, 

 the lutein cells lining it probably revert or disappear, so that finally the cysts can not be 

 distinguished from an old Graafian follicle cyst. 



In the 128 specimens from pregnant sows of which I have record, there was only one 

 case of lutein-cell cyst. In the same number of non-pregnant ovaries, containing corpora 

 lutea of ovulation, we should find 5 or 10 lutein-cell cysts. For comparison, I have looked 

 up the cases indexed as corpus-luteum cysts in the records of the gynecological service of the 

 Johns Hopkins Hospital. There were 19 cases available, all discovered at operation for 

 other conditions. One patient had passed the menopause (61 years) ; the others were from 

 16 to 42 years. 



8 had never been pregnant. 



4 had their last child or miscarriage 6 or more years before. 



5 had their last child or miscarriage 22 months to 4 years before. 

 1 had miscarried 4 months before, at the second month. 



1 had miscarried 2 weeks before, at the sixth week. 



Apparently, then, the corpus luteum of pregnancy is a comparatively less frequent 

 seat of cysts than that of non-pregnant animals, a fact in accord with the general rule that 

 abnormal alterations are less frequent in organs exercising a needed function. 



MIGRATION OF THE OVUM IN THE SOW. 



.Since the uterus of the sow is bifid nearly its whole length, it is very easy to count the 

 number of fetuses on each side. When this is done, it is often observed that there are more 

 pigs on one side of the uterus than there are corpora lutea in the corresponding ovary. In 

 a series of 117 uteri, I found 28 in which there was 1 more pig than corpora lutea on a given 

 side, 13 cases with 2 more pigs than corpora lutea on one side, and 2 in which the pigs num- 

 bered 3 more than the corpora lutea of the corresponding ovary. 



This phenomenon may be explained in three ways: (1) corpora lutea may not have 

 formed at the site of the follicle which gave rise to the supernumerary pigs; (2) there may 

 have been two or more ova in one follicle, which therefore produced two or more embryos, 

 but only one corpus luteum; (3) one or more ova may have crossed the abdominal cavity 

 and entered the opposite tube (external migration), or passed down to the junction of the 

 uterine horns on its own side and into the opposite tube from below (internal migration). 



(1) The failure of a corpus luteum to form at the site of a ruptured follicle is not 

 unthinkable, but must be very rare. In hundreds of sows' uteri I have never seen a case of 

 pregnancy without corpora lutea; nor do I know of any really unexceptionable cases reported 

 from the human or any other of the mammalia which give birth to a single infant, in which 

 such a phenomenon would be more easily detected. Fellner (1909) has mentioned one case in 

 a woman who died on the day of delivery, Ravano (1907) cites four, also from women prac- 

 tically at term, and Miller (1914) one from a case of eclampsia. Although these cases are 

 of interest otherwise, the absence of a corpus luteum at term can not be taken as evidence 

 that one had not been present earlier in pregnancy, especially since all these cases were 

 complicated by disease. 



