732 SCIENCE PROGRESS 



The credit of being the first to conduct "an experimental 

 inquiry into the factors which determine the growth and 

 activity of the mammary glands" belongs to Lane-Claypon 

 and Starling (u), who in 1906 tried the effect of the injection 

 of extracts of ovaries, placentae, and foetuses. They came to 

 the conclusion that the growth of the mammary gland during 

 pregnancy is due to the action of a specific chemical stimulus 

 produced in the fertilised ovum. Similar experiments have been 

 repeated without a uniformity of the results. 



These authors further state that the source of the stimulus 

 during early pregnancy may be located in the chorionic villi, 

 i.e. a part of the placenta. Halban (8), who gathered a great 

 deal of clinical evidence, also considers the placenta as the 

 tissue in which the chemical stimulus inciting growth in the 

 mammary glands is produced. This view, however, is open 

 to criticism. In Dasyurus, a Marsupial (14), the main growth 

 of the glands has occurred before the attachment of the embryo, 

 which does not take place until late, and therefore before the 

 formation of the placenta. In the Monotremes, the egg-laying 

 mammals, of course no placenta is ever formed : although in 

 both these cases there is a growth of the mammary glands. A 

 full functional development of these glands may be experienced 

 by virgins, and therefore without any stimulus from a foetus. 

 In hunting kennels also it is not very uncommon for a bitch 

 that has failed to become pregnant to experience such a growth 

 of the breasts that she is able to suckle the pups of another 

 mother who for some reason or other is unable to do so herself. 

 In Dasyurus the mammary glands in the non-pregnant female 

 undergo a growth identical with those in the pregnant female, 

 and reach a state of development comparable with that in the 

 mother thirty-six hours after the birth of the young. 



Although it is not improbable that the presence of a foetus and 

 its attachment may influence the very great growth and activity 

 of the mammary gland in the pregnant female, the foregoing 

 facts show that neither fertilised ovum nor placenta is necessary, 

 and therefore neither of these can be regarded as primarily 

 responsible for the production of the stimulus. Halban himself, 

 although looking to the placenta in pregnancy, admits that at 

 puberty, at the menstrual periods, and in pathological cases, 

 that is to say, cases of abnormal growths in the ovary, it is in 

 the ovary that the stimulus inciting growth in the mammary 



