i'JOG.] Growth and Activity of the. Mammary Glands. 517 



observed lined with two layers of cells, presenting the same appearance, but in a smaller 

 degree, as those in the glands of the rabbit in Experiment 1U. 



Rabbit 3. Virgin. Glands large, hypertrophied, containing a fair amount of watery 

 fluid. Alveoli present and ducts showing proliferation. 



Rabbit 4. Not virgin. Mammary glands fully marked, and distended with milkv 

 fluid, but impossible to determine whether or not hypertrophied. 



In order to be certain of the induction of growth in the mammary gland by the 

 injection of extracts of tYetus, three more experiments were made. In the first of these, 

 in which the rabbit received 16 injections of the pressed juice of the viscera of 

 138 foetuses, the results were absolutely negative. In this experiment, however, we had 

 been obtaining very small amounts of pressed juice from the tissues, and we thought that 

 the absence of result might possibly be due either to retention of the active substance by 

 the Kieselguhr or to insufficient destruction of the cells in the process of grinding. It is 

 possible, too, that immaturity of the rabbit may have been in some measure responsible 

 for the negative result. 



In the next two experiments, therefore, we abandoned the Biichner method and, after 

 grinding with sand and with normal salt solution, centrifnged and filtered the supernatant 

 liquid through a Berkefeld candle before injection. Both these experiments gave positive 

 results. 



ExperimetU 12. October 4 to -21. Virgin rabbit, full-grown. Received daily, intra- 

 peritoneally, the saline extract of the viscera of a number of foetuses about the fifteenth 

 to twentieth day of pregnancy. Killed on the 21st. It showed distinct growth of the 

 mammary glands with duct proliferation (cidv ng. .">). 



Experiment 13. October 4 to 21. Virgin rabbit. Received the saline extract, intra- 

 peritoneally, of the bodies and placentae of the same foetuses used in Experiment 12. 

 Fifteen injections were given in the 17 days. Killed on the 21st. It showed marked 

 growth of mammary glands with plentiful mitotic figures. The appearance of this gland 

 in the stained specimen is shown in fig. (5. 



Discussion of Results. 



From the results just described, it will be seen that in six eases we 

 succeeded in producing in virgin rabbits a growth of mammary glands 

 similar to that occurring during the early stages of pregnancy, and consisting 

 in the proliferation of the epithelium lining the ducts, with the multiplication 

 of these ducts by branching into the surrounding tissues. In one of these 

 (Experiment 10) where our injections were carried out during h've weeks 

 and the experiment lasted nearly seven weeks, there was an actual formation 

 towards the periphery of the gland of secreting acini. In some of these 

 cases, however, namely those in which the injections had been given under 

 the skin of the back (e.g., Experiment 9), the mammary glands were bathed 

 for considerable periods of time in the injection, and it seemed to us possible 

 that this might be a determining factor in producing growth. 



We therefore carried out a control experiment on a virgin rabbit, in which 

 normal rabbit's serum was injected, for the most part subcutaneously, for a 

 period of three weeks. The serum, which was derived from non-pregnant 

 animals, but contained much more nutrient material, e.g., proteid, than the 



