518 Dr. J. E. Lane-Claypon and Prof. E. H. Starling. [Feb. 12. 



fluids used in our previous injections, ran down in the subcutaneous tissue, so 

 that during the whole duration of the experiment the abdominal wall was 

 thickened and oedematous through the presence of the serum. On killing 

 the animal at the end of three weeks the glands were little, if any, larger 

 than those usually obtained from a virgin animal (fig. 7). On section, how- 

 ever, mitoses were present in the epithelium of the ducts, and there was 

 apparently a certain amount of proliferation of the ducts. 



We must conclude, therefore, that superabundant supply of nutrient 

 material in the fluid surrounding the acini may lead to proliferation 

 resembling in kind that which was produced by our injections. This result 

 had not been produced in an earlier control experiment, in which we injected 

 the saline extract of liver, and in view of the small results produced by the 

 injection of the serum as compared with those produced by the injection of 

 the extracts of foetus much poorer in proteids, we are inclined to believe that 

 it is impossible to explain our results in the other experiments as due to the 

 infiltration of the tissues round the glands. This explanation, at any rate, 

 could not hold for the growth in Experiment 10, in which there kad been at 

 no time any injection into the subcutaneous tissue of the back. It is 

 interesting, from the general pathological point of view, to note that typical 

 epithelial proliferation in the ducts can be produced by an abnormally large 

 supply of proteid in their surrounding lymph, and the subject is worthy of 

 further investigation. 



A striking fact in all our experiments with a positive result is the small- 

 ness of the growth produced as compared with the quantity of material 

 used for injection. In all the positive cases the material for injection was 

 derived from foetuses ; in Experiments 11 (2) and 12 from the viscera only ; 

 in Experiment 11 (3) from the bodies only ; in Experiments 9 and 13 from 

 the foetuses together with placentae; and in Experiment 10 from the foetuses, 

 placenta, and mucous membrane of uterus together. On the other hand, 

 injection of extracts made from ovaries, uterus, or placenta alone had no effect 

 on the growth of the gland. We are therefore justified in concluding that 

 under normal circumstances the hormone which is responsible for the growth 

 of the mammary gland during pregnancy is produced mainly in the growing 

 embryo. This hormone, however, must be produced in minimal quantities. 

 It is apparently not stored up in any of the tissues of the foetus or of the 

 placenta, so that, in injecting extracts of foetus, we are simply injecting the 

 small amount of material which is diffused through the juices on its way to 

 the blood-vessels and into the maternal blood. 



It is possible, of course, that the specific mammary hormone is produced 

 from a precursor or mother-substance in some organ or other, and that future 



