A HORMONE FOR GESTATION 



uterus and determines the occurrence of progestational 

 proliferation. 



The American investigator Leo Loeb had indeed already 

 shown (1909), in another way, that the corpus luteum 

 controls the state of the uterus. In the guinea pig the embryo 

 settles deeply into the uterine lining (endometrium) as it 

 does in the human species, and the maternal tissue responds 

 by active growth at the site of attachment, so that the pla- 

 centa contains a great mass of maternal cells. Loeb showed 

 that the maternal response is caused to occur by the irrita- 

 tion, so to speak, produced by the embryo as it settles into 

 the lining of the uterus. In his experiments he imitated this 

 irritative action, in nonpregnant animals, by putting into 

 the uterus, not embryos, but bits of foreign material, such 

 as tiny pieces of glass or collodion. In his simplest trials he 

 ran a silk thread through the uterus and tied it in place, 

 or merely inserted a needle into the uterus and scratched the 

 endometrium. At the points of irritation, the interior of 

 the uterus promptly developed within a few days, little 

 tumors made up of cells closely resembling, under the micro- 

 scope, the maternal part of the placenta. 



Now we come to the point of all this. Loeb discovered that 

 he could get his tumors only during a limited part of each 

 cycle, when the corpora lutea are present. If he tried at other 

 times, or if he tried it at the right time but took away the 



Plate XVIII. Action of progesterone, the hormone of the corpus luteum. 

 Af normal litter of embryos of rabbit in uterus, 5 days after mating. B, dead 

 and degenerating embryos (same age as those in ^) in uterus of rabbit whose 

 ovaries were removed the day after mating. Magnified 20 times. C, section 

 of uterus at time of ovulation. D, uterus of rabbit castrated just after ovulation 

 and given injections of progesterone for 5 days. Magnified 7 times. E, at (1) 

 section of uterus of infant rabbit 8 weeks old; at (2) same after 5 days' treat- 

 ment with estrogenic hormone; at (3) same after 5 more days' treatment 

 with progesterone. All magnified 7 times. F, two litters of rabbit embryos 

 6 days old, from mothers deprived of their ovaries one day after mating but 

 injected with progesterone daily. Magnified 71/2 times. Preparations by author. 

 Courtesy American Journal of Physiology. 



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