Abstract
Since the demonstration of Cole and Hart 1 that the blood serum of pregnant mares contains large amounts of gonadotropic hormone, this hormone has been the subject of much investigation. Although the recent work of Catchpole and Lyons 2 indicates a placental origin of the hormone, it has been found to have biological effects similar to those found in the pituitary gland and to differ markedly from the chorionic hormone of human pregnancy. Thus the experiments of Evans, et al., 3 have shown that the hormone of the pregnant mare is able to cause a marked enlargement of the ovaries of hypophysectomized rats, and it has been found to possess a pronounced stimulating effect on the testes and the comb growth of infantile cocks (Hamburger 4 ) just like the anterior pituitary hormone, while the gonadotropic hormone from the urine of human pregnancy is ineffective in this respect.
The difference between the effects of extracts of human pregnancy urine and extracts of anterior pituitary or from castrate urine on the ovary of the monkey has been previously reported (Engle, Smith and Engle 5 ).
It has been of interest, therefore, to investigate the effects of an active extract of the serum of pregnant mares on the follicular structure and activity of the ovary of the macacus monkey. Six females, 5 preadolescent and one adult, have been used in this preliminary experiment, the details of which are set forth in Table I.
The results have indicated that, regarding the functional activity and structural changes of the ovary of the monkey, the active principle of pregnant mare's serum closely resembles that found in urine of castrate women. The oestral response of the sex skin of the monkey, seen on day 5 or 6 of treatment, is quite similar to that obtained by oestrin, A.P. or C.U. (Allen, Hisaw et al., Engle), and progresses characteristically until the conclusion of treatment after 10 days. 6
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