INTERNAL SECRETION OF CORPUS LUTEUM 191 



mammary gland of Dasyurus, in which pseudo-pregnancy and 

 pregnancy are of the same length, O'Donoghue (476) came to the 

 conclusion 'that the corpus luteum is a ductless gland producing 

 a secretion which is the inciting cause of the growth of the 

 mammary gland.' Up to the present, however, administration 

 of corpus luteum preparations to the ovariectomized animal 

 has not induced a degree of mammary development com- 

 parable to that found in the normal animal during the luteal 

 phase of the cycle. This, however, is doubtless due to the failure 

 of the extracts employed up to the present to contain the active 

 principle. Preliminary experiments with the oestrus-inhibiting 

 extracts of the corpus luteum have given negative results. 

 Loeb and Hesselberg (403) failed to cause mammary develop- 

 ment by the injection of aqueous extracts of corpus luteum. 

 Champy and co-workers (119), however, have recently reported 

 the induction of mammary growth by the injection of luteal 

 extracts, while Bencan, Champy, and Keller (59) claim that the 

 corpus luteum substance can be obtained from placentae as 

 well as from the corpus luteum. The dependence of the 

 mammary gland on the corpus luteum is further shown by 

 experiments on artificial pseudo-pregnancy in the rabbit 

 (Parkes, 502). In these experiments rabbits were injected with 

 the sodium hydroxide extract of anterior pituitary and corpora 

 lutea were caused to appear in the ovary in the absence of 

 copulation. Under these conditions the growth in the mammary 

 gland typical of pseudo-pregnancy occurred. 



The development of the mammary gland during pregnancy. In 

 the rabbit, the growth of the mammary gland in the first four- 

 teen days of pregnancy is exactly the same as occurs during 

 pseudo-pregnancy. After this period, however, a completely 

 new phase of growth begins, consisting essentially in thicken- 

 ing of the gland as opposed to lateral extension. That a very 

 real difference exists between these two stages of pregnancy is 

 shown by the fact that pseudo-pregnancy in a parous rabbit, in 

 which the ducts are already well developed, produces no greater 

 growth of the gland than pseudo-pregnancy following the first 

 ovulation. 



Woodman and Hammond (644), and Asdell (43) have shown 

 that two phases of m.ammary development occur during preg- 



