1906.] Growth and Activity of the Mammary Glands. 513 



the placenta into the maternal blood-vessels. This amount we might inject 

 into our rabbits, but it would probably be taken up and absorbed into the 

 circulation of the rabbit long before we were ready for our next injection, so 

 that, whereas under normal circumstances the mammary glands are being 

 continuously stimulated to hyperplasia, we could not expect to do more than 

 give these glands a series of small shoves in the same direction. 



Methods of Experiment. 



Our object in the present research was to attempt to imitate the processes 

 of pregnancy, by the injection of fluid extracts containing the soluble con- 

 stituents of the various tissues, ovaries, uterus, placenta, or fetus into a 

 virgin rabbit. The extracts were prepared in various ways. In some of our 

 earlier experiments an emulsion of the tissue in normal salt solution, prepared 

 with aseptic precautions, was injected subcutaneously. This method limited 

 us to the use of only small portions of tissue. Since the other hormones with 

 which we are acquainted, such as secretin or adrenalin, are soluble and 

 diffusible substances, in later experiments we used a much greater mass of 

 tissue for the preparation of fluid extracts, which were made sterile and freed 

 from solid particles by passage through a Berkefeld filter. In all cases the 

 tissues were ground up thoroughly with sand. The resulting paste was then 

 in some cases mixed with normal salt solution, allowed to stand for two or 

 three hours, and centrifuged. The supernatant fluid was passed through a 

 Berkefeld filter, and the resulting clear filtrate used for injection. In other 

 cases the ground-up tissues were mixed with Kieselguhr, and the juices 

 expressed in a Biichner press ; the press-juice thus obtained was passed 

 through a Berkefeld filter before injection. The injections which were 

 naturally made with aseptic precautions were in the early experiments 

 subcutaneous. As, however, we increased the bulk of the injection, we 

 adopted the plan of injecting into the peritoneal cavity. A further advantage 

 of injecting into the peritoneal cavity is that one not only obtains quicker 

 absorption, but is free from the disadvantage attendant on subcutaneous 

 injection, namely that the fluid introduced under the skin of the back tends 

 to flow down to the subcutaneous tissue in the abdomen, so that the 

 mammary glands are bathed in an aseptic fluid containing proteids, which 

 might in itself serve as a stimulus to proliferation. 



Experiments on Injection of Tissue Extracts. 



Our experiments can be divided into the following groups according to the 

 organs injected, namely injection of ovaries, of uterine wall or mucous 

 membrane, of placentae, of placentae plus uterus, of fcetus, together with 



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