642 FKEDERICK S. HAMMETT 



from the uterine vessels a large amount of blood into the general systemic 

 circulation which played an important role in the onset of lactation. 

 Such an hypothesis is opposed by the observation that fairly normal milk 

 secretion frequently occurs, when the uterus is removed before the com- 

 mencement of lactatory activity. Schein proposed the conception that 

 milk secretion is brought about by the increased blood supply to the 

 mammae, since by the emptying of the uterus this organ has need of much 

 less blood than during pregnancy, thus allowing of its utilization by the 

 upper half of the body and particularly the mammae. There is, however, 

 no positive proof for this hypothesis and certain facts oppose its proba- 

 bility. For instance, when abortion occurs, even during the early stages 

 of pregnancy, and at a time when the blood supply to the gravid uterus 

 is not much greater than normal, secretion of milk is frequent ;. moreover, 

 removal of immense ovarian and uterine tumors is not followed by any 

 increased activity of the mammary glands, insofar as secretion is con- 

 cerned, although such procedure must materially alter the distribution of 

 the blood in the body ; since neither nerve impulses nor augmented circula- 

 tion account for lactation it seems probable that a qualitative change in 

 the blood constituents in the nature of hormone stimulation is the under- 

 lying factor concerned. 



Inasmuch as the factors concerned in the pubertal, menstrual and preg- 

 nancy growth impulse are rather definitely established, as well as the 

 source of the stimulus to lactation, whereas the first or embryonic impulse 

 is more or less a matter of conjecture, this latter phenomenon will be 

 briefly discussed and the later stages taken up under the discussion of the 

 relations of the secretions of the individual endocrin glands to the different 

 periods of mammary activity. 



Halban (1005), noting the occurrence of hypertrophy of the fetal 

 mamma during the eighth and ninth months of intra-uterine life, attrib- 

 uted it to the stimulating influence of a placental hormone derived par- 

 ticularly from the trophoblast and chorionic epithelium. This opinion 

 was based on the hypothesis that the mammary hyperplasia of pregnancy 

 is due to a placental secretion. The hypothesis lacks exact confirmation, 

 and is, indeed, improbable. 



Hormone Factors in Mammary Activity 



The Ovary and Mammary Activity. Pubertal Growth Impulse. 

 That the normal development of the mammae at puberty is dependent upon 

 an ovarian function is demonstrated by the experiments of Knauer (a) (&) 

 (c) (1896-1900), who found that if ovarian transplantation was followed 

 by atrophy, the mammary development did not occur. Halban ' (a} (ft) 



