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mucous membrane and muscle. Moreover there is formed, partly from 

 foetal and partly from maternal tissues, an organ of highly complicated 

 structure the placenta the express object of which is the nourishment 

 of the growing young animal. It is evident that the chemical stimulus or 

 hormone for the growth of the mammary gland may be manufactured in 

 any of these four organs the ovary, uterus, placenta, or foetus and that, 

 in fact, two or more of these might cooperate in producing the effective 

 stimulus for the mammary gland. The experimental solution of the 

 question must therefore be a lengthy one. Even if we were certain of the 

 seat of origin of the specific hormone, we should have to imitate the con- 

 stant leakage of this substance into the maternal organism and to continue 

 our experiments over a long period in order to produce artificially any 

 growth of the mammary glands. It is impossible, in a short experiment, 

 to prove the presence of a growth-compelling hormone in a fluid, as is so 

 easily done in the case of substances, such as adrenalin or secretin, 

 which increase the functional activity of any given tissue. There 

 are a few clinical facts which, though not decisive, give an indication of 

 the direction in which we may seek solution. Thus, in extra-uterine 

 pregnancy, the growth of the mammary glands occurs as usual, although 

 there is only a relatively slight hypertrophy of the uterus and its mucous 

 membrane. If, under these conditions, death of the foetus occurs, growth 

 of the mammary glands at once ceases, although no definite change has 

 taken place in the uterus. We shall be therefore inclined to locate the 

 origin of the hormone either in the foetus or in the foetal part of the 

 placenta. The influence of the ovary on the growth of the mucous mem- 

 brane of the uterus and on the attachment of the foetus has been already 

 mentioned. This influence is apparently exerted by the luteal tissue. 

 Since the corpora lutea atrophy during the latter half of pregnancy i.e., 

 at a time at which the growth of the mammary gland is most rapid, it 

 seems unlikely that the ovary will elaborate the specific hormone in ques- 

 tion, though the possibility must be excluded by special experiments. For 

 the past 12 months I have been engaged with Miss Lane-Claypon in an 

 endeavour to determine the origin and nature of the specific stimulus 

 which occasions the growth of the mammary glands during pregnancy. 

 In a preliminary series of experiments one rabbit was injected every day 

 for a fortnight subcutaneouslyand intraperitoneally with an emulsion pre- 

 pared by grinding up the ovaries from pregnant rabbits. Another rabbit. 

 also a virgin, received a similar emulsion prepared from the placenta 

 and uterine mucous membrane from a series of pregnant rabbits. Each 

 rabbit received about ten injections from as many pregnant rabbits. In 

 no case, however, was any effect produced on the mammary glands. 



These negative results caused us to try the influence of extracts made 

 from the body of the foetus itself. The large size of the foetuses, how- 

 ever, rendered it impossible to adopt the method we had previously been 

 using i.e., the injection of emulsions. The injection of emulsions of 

 tissues, either subcutaneously or intraperitoneally, is, moreover, fraught 

 with considerable risk of suppuration, even though scrupulous precautions 



