522 Growth and Activity of the Mammary Glands. 



We cannot, however, claim that these conclusions of ours are firmly 

 established. A final decision can only be given by a research carried on 

 under more favourable conditions. One requires, in fact, a farm, where we 

 could have at our disposal 500 rabbits, and could arrange for a plentiful 

 supply each day of rabbits about the middle of pregnancy. Under these 

 conditions it might be possible to determine both the seat and nature of the 

 effective stimulus, as well as to test the influence of various reagents in 

 splitting off the hormone from some possible precursor. Many of our 

 experiments, carried out in a London laboratory, were brought to a premature 

 conclusion by failure of material. If, however, the Conception of the action 

 of the mammary hormone, which was put forward by Hildebrandt and adopted 

 by us, is correct, namely, that it is a substance which produces growth by 

 inhibiting the normal activity of the gland cell, it should be possible to 

 decide many questions affecting it by working on an animal, such as the goat, 

 in lactation. Injection of the hormone should diminish or stop the 

 secretion of milk while it was circulating in the blood, but should, as a 

 secondary effect, produce an increased secretion as a reaction from the 

 immediate assimilatory effect. The injection might, indeed, have to be 

 prolonged for one or two days, since we know that in Man the onset of a 

 renewed pregnancy during lactation stops the flow of milk only after some 

 time (three or four weeks). At any rate, such experiments could be more 

 rapidly carried out than those which have been the subject of this com- 

 munication. 



DESCRIPTION OF PLATE. 



The drawings were made as follows : — The mammary glands were dissected out, pinned 

 on corked rings, hardened in corrosive sublimate and formol, washed, and stained in very 

 dilute haematoxylin. They were then dehydrated, cleared, and mounted as lantern slides 

 in Canada balsam between glass plates. (These specimens were shown by projection at 

 the meeting of the Royal Society, on March 1, 1906.) An image of the specimens was 

 thrown (without magnification) on to a piece of millboard, and the darkly stained glands 

 were traced out in indian ink. The figures, therefore, reproduce the glands in natural 

 size. 



Fig. 1. — Gland from virgin rabbit. 

 „ 2. — Mammary gland from primiparous rabbit, five days after impregnation. 

 „ 3. — Mammary gland from primiparous rabbit, nine days after impregnation. 

 „ 4. — Mammary gland from virgin rabbit which had received injections of extracts 



of foetuses, uterus, and placentae during five weeks (Exp. 10). 

 „ 5. — Mammary gland of virgin rabbit, showing growth produced by injection of 



extracts of foetal viscera during a period of 17 days. 

 „ 6. — Mammary gland of virgin rabbit, showing growth produced by injection of 



extracts of foetal bodies and placentae over 17 days. 

 „ 7. — Mammary gland of virgin rabbit, showing slight growth induced by daily 



subcutaneous injection of rabbit's serum (from non-pregnant rabbits) during 



a period of three weeks. 



