LACTATION 619 



(p. 374), and then finding that the development of the glands was 

 never in excess of what takes place under the influence of the 

 corpora lutea of pseudo-pregnancy. Moreover, he found that in 

 rabbits in which the foetuses were removed but the placentas 

 retained there were no secondary growth changes in the milk glands. 

 Biedl and Koenigstein 1 had already shown that implantation of 

 placenta was without effect on the glands but that transplantation 

 of the foetus resulted in mammary growth and the secretion of 

 inilk. 



Hammond found also that, contrary to the generally accepted 

 opinion, the corpus luteum in the rabbit is fully persistent and 

 therefore active during the second half of pregnancy. This con- 

 clusion is based on a series of measurements of corpora lutea at 

 different days after copulation in pregnant and pseudo-pregnant 

 individuals, and in others in which decidual cells had been experi- 

 mentally produced or in which the fetuses had been removed. It 

 was found that the corpora lutea, after the sixteenth day, retained 

 their size only in pregnant rabbits and in these underwent some 

 further development ; in the other three series they underwent a 

 very marked regression. Hammond concluded, therefore, that the 

 development of the mammary glands of the rabbit during the second 

 part of pregnancy is under the same influence as that which con- 

 trols it during the first half, namely, the corpus luteum, and that 

 the further development and persistence of the latter organ in the 

 last part of gestation is due to the presence of the foetus. 



In the virgin rabbit, as already mentioned, the mammary tissue 

 before ovulation is limited to a few small ducts in the immediate 

 vicinity of the nipple, no true growth taking place until the corpus 

 luteum begins to develop. In polyoestrous animals which ovulate 

 spontaneously, on the other hand, notwithstanding the fact that 

 they do not experience pseudo-pregnancy (excepting possibly in a 

 very abbreviated form), mammary tissue may be built up even in 

 the virgin to such an extent that at a certain stage fluid secretion 

 occurs. This has been shown to be so by Woodman and Hammond 2 

 in the virgin heifer, in which mammary activity was found to take 

 place during the oestrous cycle. In such animals they found in the 

 udder the characteristic proteins (caseinogen, globulin, and albumen) 

 of colostrum, together with small amounts of fat, lactose, and 

 proteose. 



The correlation between the generative organs and mammary 

 glands in the guinea-pig has been deal-t with in a series of papers 



1 Biedl and Koenigstein, "Ueber das Mammahormon," Zeitsch. f. Exp. Path, 

 und T/ter., vol. viii., 1910. 



2 Woodman and Hammond, " Note on the Composition of a Fluid obtained 

 from the Udders of Virgin Heifers," Jour, of Agric. Science, vol. xii., 1922. 



