148 The Endocrine Organs 



arrested, and it is inferred that their secretion is necessary for such develop- 

 ment. It must, however, be pointed out that it is next to impossible to 

 destroy the corpora lutea without practically destroying all the ovarian 

 tissue, for the corpora lutea of the pregnant rabbit form by far the 

 greater mass of the ovary. This applies also to Fraenkel's experiments 

 (see below). 



An important function of the internal secretion of the ovary — perhaps 

 of the corpus luteum — relates to the formation of the uterine decidua 

 and the fixation of the embryo. Fraenkel — working upon a hypothesis 

 suggested by Born — found that if in rabbits the corpora lutea are destroyed 

 at an early period of pregnancy the embryo does not become adherent to 

 the mucous membrane of the uterus, and ceases to develop. Marshall and 

 Jolly, working with dogs and rats, obtained similar results from double 

 ovariotomy in early pregnancy. L. Loeb observed that mechanical stimuli 

 are able to produce the formation of decidual membrane and uterine hyper- 

 plasia if corpora lutea are present in the ovary, but that there is no such 

 change in their absence. Extracts of corpus luteum are not in this respect 

 able to replace the functions of the removed organs. 



Loeb has shown that in the guinea-pig extirpation of the corpora 

 lutea accelerates bursting of the ripe Graafian follicles, i.e. is conducive to 

 ovulation ; this suggests that their presence militates against ovulation. 



Internal Secretion of Uterus 



There is some evidence that in certain states the uterus itself may 

 yield an internal secretion. Blair Bell has suggested that menstruation 

 and ovulation depend on such a secretion, and Bond has described experi- 

 ments which appear to indicate that an internal secretion from the uterus 

 promotes the growth of the corpus luteum. But these views find no 

 support in the experiments of Carmichael and Marshall, who obtained typical 

 development of the ovaries, with ovulation and formation of corpora lutea, 

 in animals (young rabbits and adult rats) from which the uterus had been 

 completely removed. Bouin and Ancel have described an epithelium-like 

 formation in the muscular coat of the uterus of the rabbit and guinea-pig 

 during the latter half of pregnancy which they consider to be related to 

 the development of the mammary glands during the final period of gestation 

 and the production of milk. To this formation they have given the name 

 of " glande myometricale endocrine." Mackenzie found that extracts from 

 the involuting uterus of the cat shortly after parturition cause a free flow 

 of milk from the incised nipple of lactating animals (fig. 103). He obtained 

 no such results with extracts made from the non-pregnant uterus, or from 

 the pregnant uterus at other times. He infers, therefore, that the uterus 

 contains a galactagogue hormone only at this period. 



