580 THE PHYSIOLOGY OF REPRODUCTION 



This parallelism is said to exist even in the absence of 

 pregnancy. 1 



Miss Lane-Claypon and Starling appear to have been the first 

 to deal with the problem experimentally. In an initial series 

 of experiments they injected extracts or emulsions of ovaries 

 obtained from pregnant rabbits into other rabbits either sub- 

 cutaneously or intraperitoneally. In two further series of 

 experiments rabbits were injected with uterine and placental 

 emulsions or extracts. In no case, however, did the injections 

 produce any effect on the mammary glands, although in certain 

 of the experiments in which ovarian or uterine substance was 

 employed, marked swelling and congestion of the uterus were 

 afterwards observed. 



The effect of injecting foetal extract was next tried, and this 

 led to definite positive results. When repeatedly injected into 

 female rabbits the extract was found to produce a genuine 

 development of the mammary glands which simulated the 

 normal growth which occurs during pregnancy. In one case a 

 virgin rabbit received fifteen injections of extract made from 

 many embryos of the same species. The injections were spread 

 over a fortnight, at the end of which the rabbit was killed. It 

 was found that a secretory fluid could be expressed from the 

 nipples, and that on reflecting the abdominal skin all the 

 mammary glands had grown to the size which is ordinarily 

 reached in a rabbit about eight days pregnant. In another 

 rabbit which received twenty-four injections, spread over five 

 and a half weeks, the effects produced were still more marked. 

 Further experiments showed that boiled extract was as effective 

 as unboiled, and the conclusion is therefore drawn that in all 

 probability the specific secretion or hormone is capable of with- 

 standing boiling. It was shown also that the substance in 

 question could be obtained equally well from different parts of 

 the foetus, that it passes through a Berkefeld filter, and that it 

 is not retained to any appreciable extent by the kieselgur in 

 Buchner's method for extracting cell juices. 



Foa, states that extract of ox foetus, when injected into rabbits, 

 produced development of the mammary glands. He concludes, 

 therefore, that the stimulating substance which ciuses mammary 



1 See page 343. 



