A HORMONE FOR GESTATION 



By 12:20 p.m. the uterine muscle was practically not con- 

 tracting at all. This effect wears off in a few hours. 



Such a sedative action of progesterone upon the uterine 

 muscle has been observed in many animals and there seems to 

 be good evidence that it occurs in the human species. In all 

 probability it serves to keep the uterus quiet in early preg- 

 nancy so that the embryos can become safely implanted. 



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Fio. 18. Effect of progesterone on the contractions of the living rabbit's 

 uterus. A tiny rubber bulb in the cavity of the uterus is compressed each 

 time the uterine muscle squeezes down, so that the rhythmic contractions 

 are recorded on a revolving drum. Progesterone administered at 10:20 

 a.m. By 12:20 p.m. the uterus is quiescent. From an article by S. R. M. 

 Reynolds and W. M. Allen, 1935, by courtesy of the American Journal 

 of Obstetrics and Gynecology and the C. V. Mosby Company. 



Is the corpus luteum necessary throughout pregnancy? 

 In the rat and mouse, removal of the ovaries at any time in 

 gestation causes termination of pregnancy. The embryos are 

 cast off prematurely or they break down in the uterus and are 

 absorbed in situ. Guinea pigs do not always lose their young 

 if the ovaries are removed after implantation has occurred. 

 In humans it seems certain that both ovaries, including of 

 course the corpus luteum, can be removed after the first few 

 weeks without harm. ^Vhether the pregnant human female, 

 and other animals having long terms of pregnancy, do not 

 need progesterone after the embryos are safely implanted, or 



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