LACTATION 



617 



There is always a hypertrophy followed by a secretion of milk, and 

 superficially it is impossible to distinguish pseudo-pregnancy from true 

 pregnancy. Moreover, in the dog, 1 which also ovulates spontaneously, 

 pseudo-pregnancy may follow the discharge of the ova, the corpus 

 luteum persisting and the mammary glands undergoing growth 

 followed by secretion, a fact which explains the observations of 



FIG. 168. Photograph of mammary tissue of virgin rabbit. The mammary 

 development is limited to a few ducts. (From Hammond and Marshall.) 



FIG. 169. Photograph of mammary glands of pseuda-pregnant rabbit 

 fourteen days after oestrus. The rabbit had never bred. (From 

 Hammond and Marshall.) 



Heape and others that even virgin bitches frequently lactate and are 

 capable of suckling litters of pups produced by other individuals. 



The hypertrophy of the mammary glands in the pseudo-pregnant 

 rabbit culminates at about the sixteenth day, after which time it begins 

 to regress, but milk may be expressed from the nipples from the 

 nineteenth day onwards for a week or so, and even in individuals 

 which were previously virgins, while, as already mentioned, on 



1 Marshall and Hainan, "On the Post-CEstrous Changes occurring in the 

 Generative Organs and Mammary Glands of the Non-Pregnant Dog," Proc. Roy. 

 Soc., B., .vol. Ixxxix., 1917. 



2O A 



