LACTATION 



617 



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

 superficially it is inipossilile to distinguish pseudo-pregnancy from true 

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

 pseudo-pregnancy ma)- 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 



'--^« 



Fio. 168. — Pliotoo-iaph of maiumary tissue of virgin rabbit. The mammary 

 de\'elopiueiit is limited to a tew ducts. (From Hammond and Marshall.) 



Fro. 109. — Photograph of mammary glands of pseudo-pregnant rabbit 

 fourteen days after (estrus. The labliit had never bred. (From 

 Hammond and Mar.shall.) 



Heape and others that even virgin bitches frequently lactate and are 

 capable of suckling litters of pups produced by other individuals. 



The liypertrophy of the mammary glands in the pseudo-pregnant 

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

 to regress, l)ut milk may 1ie expressed from tlie 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-(-Estrous Changes occurring in the 

 Generative Organs and Mammary ( Hands of the Non-Pregnant Dog," I'roc. Roy. 

 Soc, B., vol. ixx.xix., 1917. 



