PHYSIOLOGY, CHEMISTRY AND PATHOLOGY 567 



causes earlier and more extensive degeneration of those which develop. 

 The necrosis is largely due to hemorrhage. But deciduomata produced 

 by mechanical means in one horn of a uterus while the other horn is 

 pregnant may persist throughout pregnancy. This appears to be due 

 to a distant effect either of the embryo or the yellow body. If it is 

 due to the latter, then it is clear that it cannot be due to the continuation 

 of the same secretory activity which calls forth the deciduomata, for 

 at the time when the life of the deciduoma is thus being prolonged, the 

 sensitizing substance is no longer produced in the corpus luteum. Either, 

 therefore, there are two quite different actions of the yellow body secre- 

 tion, one sensitizing the uterus, the other prolonging the life of the 

 deciduoma, or there is only one substance, but this is poured out in dif- 

 ferent quantities at different periods. The small quantity at the later 

 period is sufficient to preserve deciduomata, but would be insufficient for 

 the new formation of these growths. 



Function of the Corpus Luteum Influence on the 

 Growth of the Mammary Gland 



We have seen that the corpus luteum inhibits ovulation, and that it 

 has a sensitizing action on the uterus. Incisions into the uterus made 

 from two to nine days after coitus or after rut, that is to say, at a period 

 when the yellow body has been active for some time, are followed by 

 the appearance of multiple tumors along the line of incision. These 

 have the same microscopical structure as the maternal placenta. The 

 mechanical stimuli, therefore, assume in this respect the function which the 

 ovuni exerts under normal conditions. But the corpus luteum appears to 

 have also another important function related to the mammary gland. 



Hildebrandt suggested that during pregnancy an impulse is exerted by 

 the developing ovum on the mammary glands, which acts as a stimulus 

 to growth and at the same time protects the cells of the gland from 

 those autolytic disintegrative processes which occur to a large extent in 

 the secretory gland. The matter was put to the test by Lane-Claypon 

 and Starling. These observers made extracts of fetuses by rubbing up 

 with sand, extracting with normal saline solution, centrifuging, and pass- 

 ing through a Berkefeld filter. The animals used for experiment were 

 then injected subcutaneously with the extracts. In virgin rabbits a 

 growth of mammary gland was produced, and in multiparous animals 

 a secretion of milk. The authors believe that their experiments show 

 that the growth of the mammary glands during pregnancy is due to the 

 action of a specific chemical stimulus ("hormone") produced in the fer- 

 tilized ovum. The amount of this substance increases with the growth 

 of the fetus and is largest during the latter half of pregnancy. Foa (&) in 



