866 J. A. MYERS 



A point which has been discussed at some length recently and 

 one which has proved to be of considerable importance in experi- 

 mental work is that of the variation in the relative size and de- 

 velopment of the various glands in the same individual, and of 

 glands from different individuals of the same age. Lane-Clay- 

 pon and Starling ('06) in working on the growth and activity of 

 the mammary gland concluded that. breast hyperplasia of preg- 

 nancy is caused by chemical substances formed in the embryo. 

 Such substances passing through the placenta into the maternal 

 blood-stream cause growth of the mammary gland. To decide 

 definitely as to just what tissues cause this growth Lane-Claypon 

 and Starling injected extracts of placenta, placenta and uterus, 

 ovaries, fetus, fetus together with the placenta and membranes, 

 and mucous membrane of the uterus into virgin rabbits. Some 

 of the extracts when injected caused very little apparent change 

 in the size of the mammary gland of virgins, while others (fetus 

 extract, for example) seemed to cause a marked development of 

 the glands. 



Frank and linger ('11) in repeating certain of Lane-Claypon 

 and Starling's experiments obtained different results, and further- 

 more found that their own series of experiments did not show 

 uniform results. Thus they concluded that some disturl^ing fac- 

 tor remained to be accounted for, so they decided to study more 

 carefully the anatomy and the physiology of the normal mam- 

 mary glands of the rabbit. For such study they selected a num- 

 ber of apparently virgin adult female rabbits and under the 

 necessary precautions removed a mammary gland from each. 

 At various intervals of time other mammary glands from the 

 same animal were removed and studied. From these experi- 

 ments Frank and Unger were able to demonstrate in virgin rab- 

 bits changes which were indistinguishable from those seen at the 

 end of the first third of pregnancy. Thus some physiological 

 factor must be involved. Frank and Unger found a partial ex- 

 planation for this condition in an article by Bouin and Ancel 

 ('09) who describe variation in the size and appearance of the 

 rabbit's mammary gland corresponding to the development of 

 the corpus luteum. A little later O'Donoghue ('12) showed that 



