THE GENERATIVE GLANDS 375 



among animals, in which hyperplasia of the lactic -glands persists 

 for a short time after parturition. Basch states that he was 

 unable to obtain hyperplasia of the mammary glands of virgin 

 animals by the implantation of placental tissue. But the 

 implantation of the ovaries from a pregnant bitch under the skin 

 of the back of a i-year-olcl nulliparous bitch, was followed, fourteen 

 days later, by proliferation of the mammary gland of the latter ; 

 at the end of six weeks the enlargement was considerable ; and 

 after eight weeks secretion of milk was induced by the injection 

 of placental extract. Microscopic examination revealed the per- 

 fect picture of a gland in full secretory activity, while at the same 

 time the uterus retained its virgin character and the ovaries were 

 very small. Basch concluded that the hyperplasia of the 

 mammary gland in pregnancy depends upon certain chemical 

 substances, which are developed in the ovary, and which prepare 

 the gland for prolonged functional activity. 



It is difficult to reconcile this assumption of Basch's with the 

 observations of other authors, which show that the internal 

 secretory activity of the ovary is inhibited during pregnancy. It 

 is, moreover, inconsistent with the fact that the hypertrophy of 

 the mammary glands is sometimes unaffected by castration at an 

 early stage of pregnancy. That the enlargement of the mammae 

 at puberty and during menstruation is the result of ovarian 

 influence, is not to be denied; but the cause of the hypertrophy 

 of pregnancy must be sought, not in the ovary, but in the foetus 

 which develops from the fertilized ovum. 



Before solving the further question, namely, as to why the 

 secretion of the hyperplastic gland does not commence until after 

 parturition, we must consider what happens upon suppression of 

 the ovum, that is, of both foetus and placenta. It has long been 

 known that after intra-uterine death of the ovum milk forms in 

 the mammary glands and the lacteal secretion begins. The same 

 thing happens if the foetus is removed by surgical methods during 

 the second half of pregnancy. Halban concluded from this that 

 the important factor lay, not in the death or removal of the foetus, 

 but in the removal of the placenta, and that it was the biological 

 suppression of the placenta which supplied the impulse to the 

 secretion of milk. He and others find confirmatory evidence of 

 this theory in the "witches' milk" of new-born infants, which 

 they regard as the expression of the puerperal involution of the 

 fcetal organs, which had previously reacted to the conditions of 

 pregnancy. 



Basch found that, by the subcutaneous injection of placental 

 extract, he was able to produce secretion of milk, sometimes in 

 considerable quantities, in animals in which the enlargement of 

 the mammae had persisted after the termination of pregnancy ; he 

 regards the results of these experiments as proof of the depen- 

 dence of the lactic secretion upon a substance found in the 



