THE OVARY AS TIMEPIECE 



The method was soon applied to the rat by Long and Evans 

 of the University of California and to the white mouse by 

 Edgar Allen of Yale Medical School, then at Washington 

 University, St. Louis. We shall see in subsequent chapters 

 some of the important work that was made possible because 

 the cycles of these three animals were now so much better 

 known. The detection of the ovarian estrogenic hormone by 

 E. Allen and Doisy (1923) was a direct result; so was the 

 discovery of Vitamin E by H. M. Evans and his colleagues 

 (1922). In conjunction with the growing knowledge of the 

 cycle of the sow and of reproduction in the rabbit, it led 

 indirectly to the discovery of the corpus luteum hormone and 

 to a far clearer general comprehension of the whole field than 

 was possible before. 



The exact details of the vaginal changes are of no particu- 

 lar importance except to those who need to follow them in the 

 laboratory. Briefly stated, there are two kinds of cells that 

 get free in the vagina. One kind is of course the cells of its 

 lining. These are epithelial cells like those of the external 

 skin except that they are ordinarily moist. Those that lie on 

 the surface of the lining are not infrequently shed into the 

 cavity. The cyclic changes can be followed in the accompany- 

 ing figure, taken from the monograph on the rat's cycle by 

 Long and Evans. In Plate XIII, B we see the vaginal cells 

 as they are in the interval or diestrous phase ; there are fairly 

 large numbers of white blood cells or leucocytes (the small 

 rounded cells with irregular nuclei) intermingled with a few 

 large flat epithelial cells. At C we see signs of approaching 

 estrus; the leucocytes have disappeared, and the epithelial 

 cells are swollen and rounded, by action of the ovarian hor- 

 mone upon them before they were shed from the wall into the 

 cavity of the vagina. In figure D of Plate XIII we see that the 

 epithelial cells now being shed are dry, scaly, and lack nuclei 

 — they are cornified, as we say, like the cells on the dried-out 

 surface of ordinary skin. At the time when the ripe follicles 



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