140 CYCLIC CHANGES IN THE OVARIES AND UTERUS OF THE SOW, ETC. 



During the last days before the onset of oestrus, however, a few mitotic figures 

 are found in the surface epithelium and at the same time there are numerous points 

 of vacuolar degeneration of the epithelial cells. The most remarkable event of this 

 stage is the assembling of large numbers of neutrophil leucocytes in the subepi- 

 thelial stroma. In some of the specimens (fig. 23, pi. 3), the leucocytes are seen 

 swarming out of every arteriole in the superficial stroma and passing toward the 

 epithelium; a little later they are arranged along the bases of the epithelial cells 

 and a few are to be found passing through toward the lumen. An cedematous 

 state of the stroma also sets in toward the end of this period, and thus, by a combi- 

 nation of all these changes, the uterine mucosa is brought up to the cestrous stage, 

 at which we began the description. 



To conclude this cursory description of the uterine cycle, it may be added that 

 the histological changes are not without effect on the general appearance and tex- 

 ture of the uterine mucosa. An opened uterus taken during the cestrous period is 

 paler than at other times, with a firmer and at times slightly gelatinous inner sur- 

 face (due to the oedema) ; while during the rest of the cycle, and perhaps especially 

 from the ninth to the tenth days, the mucosa is pink or red, soft, and velvety. 

 There is also a periodic change in the external dimension of the uterus, for, by 

 plotting the circumferences (at the mid-points of the cornua) of the uteri of our 

 22 mature sows of similar age, in the order of their cyclic stages, a significant curve 

 is obtained which is directly correlated with the degree of oedema of the stroma. 

 In other words, the uterus is slightly larger just before and during the period of heat, 

 because the stroma is then thickened by cedema. Caution must be used, however, 

 in the interpretation of measurements and gross appearances as seen in specimens 

 obtained at random at the slaughter-house, for there are numerous possibilities of 

 uncontrollable variation, especially in the amount of bleeding of the carcases and 

 in the ages of the animals. Some are taken very young, even before the first 

 oestrus, and therefore long before the uterus has attained full development. A 

 marked state of oestrous cedema does not seem to occur at the earliest heat periods. 



For the same reason I have refrained from dogmatic statements on a point of 

 some interest namely, whether there is a postcestrous hypertrophy of the glands, 

 such as has been described, for instance, by Keller (1909) in the dog. Study of 

 our 22 animals of known age and comparable size, though suggesting a positive 

 answer, does not suffice to settle this question, since there are wide variations in the 

 number of glands, and one is further confused by the difference in fluid-content of 

 the stroma. It is difficult to compare specimens in one of which the glands are 

 widely spaced and the stroma thick, while in the other the glands are densely 

 packed in a narrow space. 



Another uncertain matter concerns the numerical relations of the epithelial 

 cells. There is a period of very active proliferation of both surface and glandular 

 epithelium, but no time of widespread destruction. One is forced to assume for the 

 present that the postcestrous wave of mitosis is compensated for by the sporadic 

 degeneration of epithelial elements, which must be very frequent if the compressed 

 cells (page 138) are, as suggested, in a moribund or degenerated state, and by the 

 loss of cells due to the vacuolar degeneration of the precestrous and cestrous periods. 



