1906.] Growth and Activity of the Mammary Glands. 519 



research may reveal some method of splitting off the hormone in large 

 quantities, and also of determining whether its production is diffused through- 

 out all the tissues or is confined to one special organ of the body. Injection 

 of extract of duodenal mucous membrane, for example, would give only 

 minimal effects on the pancreas. We should not be justified in concluding 

 from this absence of result that the duodenum was not the seat of origin of 

 the chemical stimulus to the pancreas. Its peculiar relation to the pancreas 

 is only brought into prominence when it is treated with acid, so as to liberate 

 the secretin from its mother substance. 



Our experiments, therefore, throw no light on the seat of production of 

 the hormone in the foetus. Apparently the extent of the growth obtained is 

 a function of the quantity of tissue used in preparing the extracts. The wide- 

 spread occurrence of the substance in the body of the foetus points to its 

 being extremely diffusible, as indeed we should expect from analogy with 

 other hormones. 



We can only say, therefore, that the hormone is produced by some or all 

 the tissues of the fertilised ovum, whence it is carried off by the blood to the 

 placenta, and so makes its way by diffusion into the maternal blood-vessels. 

 Whether it is identical with the substances which are responsible for the 

 production of the other changes associated with pregnancy, or whether there 

 are distinct substances acting on each organ which is modified during this 

 condition, our experiments do not show. But we have evidence that in the 

 foetus itself the hormone or hormones of pregnancy have the same result as 

 in the maternal organism. Thus there is increased growth of the mammary 

 glands in the foetus during the last month of pregnancy, and also in the 

 female an increase in the uterine mucous membrane, as has been shown by 

 Halban. After birth the mammary glands may begin to secrete just as after 

 pregnancy, and there are changes in the uterine mucous membrane similar to 

 those associated with menstruation. 



Are we to regard, then, the foetus as the only source of this hormone ? 

 The facts mentioned at the beginning of this paper show that such a 

 conclusion is impossible. The growth of the mammary glands which occurs 

 at puberty can only be ascribed to ovarian influence, and is absent if the 

 ovaries have been previously removed, and Halban ascribes to this ovarian 

 substance both the growth of the mucous membrane during each pro-cestrus 

 and the swelling of the glands at each oestral period, which may in rare cases 

 be attended or followed by the actual formation of milk. Halban explains in 

 the same way those cases recorded by Heape and Kehrer, in which bitches, 

 which had not been impregnated at the normal time, have, after two months, 

 not only made a bed for their young, but have had swelling of the mammary 



