PKACTICAL PAPERS—ABORTION IN COWS. 
263 
paratus; and one very large class, the mammalia, is character¬ 
ized by the presence of an organ—the udder or mammary gland 
—whose primary and natural function is to secrete a fluid for 
the nourishment of the young, immediately, and for a future 
variable period after birth ; which fluid is also derived from the 
blood of the parent. 
The uterus and mammary gland bear a certain inverse rela¬ 
tionship to each other, with regard to their activity and func¬ 
tion ; the one, in the natural condition being comparatively 
quiescent when the other is active. In this condition, during 
the development of the embryo—in other words, the preg¬ 
nancy of the dam—the uterine organs are in a state of ex¬ 
treme activity, all other parts of the animal economy tending to 
the proper performance of this tunction; and the mammary 
gland, though showing evidence of being influenced by this 
process, is in the early stages, inactive. But as pregnancy 
advances to its natural terminaiion, and preparations are being 
made for the change that is about to occur, the most marked 
of theseus the increase in the activity of the mammary gland, 
which either just before or very soon after delivery secretes 
the milk designed to be the food of the young animal, when¬ 
ever the more intimate placental connection i^ severed. The 
young animal, after birth, at first depends upon the milk 
entirely for its nourishment, and the supply of blood, before 
furnished to the plancenta, is now direeted to the mammary 
gland. But as the growth of the young animal enables it to 
look elsewhere for food, it makes less demand upon the dam; 
the supply of milk diminishes in quantity, and the uterine 
organs, having had an opportunity to return to their previous 
condition^ are again stimulated to the performance of tjaeir 
natural function ; and when pregnancy again occurs, the blood 
is redirected to the uterus and^ the mammary glands diminish in 
activity^ soon become quiescent, and the same series of phe¬ 
nomena are again repeated. 
In this hasty sketch of the main points in the history of the 
reproductive process, as it occurs naturally, uninterfered with 
by habits of domestication, your attention is ealled to the 
