192 INTERNAL SECRETIONS OF THE OVARY 



nancy in the cow and the goat. In nulHparae a great develop- 

 ment of the alveoH begins about midway through pregnancy and 

 this is correlated with a change in the type of secretion found in 

 the gland. Before this stage the secretion is of a serous nature 

 and has the characteristics of diluted milk. At the midway 

 stage the secretion changes abruptly to a thick pigmented fluid 

 containing up to 40% of solids, mostly globulin. Drummond- 

 Robinson and Asdell (171) found that the removal of corpora 

 lutea in the goat did not result in milk secretion, unless the 

 operation was performed after the globulin stage had been 

 reached. 



In the guinea-pig, also, two phases of mammary growth 

 during pregnancy have been described by Loeb and Hesselberg 

 (403) . For the first twenty-four days of pregnancy (out of sixty) 

 the mammary gland is more or less quiescent (as in the luteal 

 phase of the dioestrous cycle) ; from this stage onwards 

 continuous growth takes place. 



The cause of the final development during pregnancy. The 

 initial growth of the mammary gland during pregnancy, 

 corresponding to the growth found during pseudo-pregnancy, is 

 clearly under the influence of the corpus luteum, but for various 

 reasons it has often been thought that the growth taking place 

 during the second half of pregnancy requires some additional 

 stimulus. It has been supposed, for instance, that the corpus 

 luteum does not function during the later stages of pregnancy 

 and cannot, therefore, exert an influence on the mammary gland. 

 It has also been pointed out that the growth of the mammary 

 gland during pseudo-pregnancy, when no foetuses are present, 

 does not equal that occurring during true pregnancy. For these 

 reasons the theory has been held that some foetal or other extra- 

 ovarian stimulus is required for the complete growth of the 

 mammary glands. Lane-Claypon and Starling (341) reported 

 experiments on the injection of foetal and placental extracts into 

 virgin rabbits. These experiments seem to show that some 

 growth could be produced by such means, but their illustrations 

 make it quite clear that the amount of development produced 

 was far less than that normally found during pseudo-pregnancy 

 and consequently less than takes place under the influence of the 

 corpus luteum alone. Ancel and Bouin (33) ascribe the later 



