Abortion in Coivs. 201 



work or functions. And this is what actually happens to 

 the udder-supply arteries from over-rapid expansion by 

 very hasty engorgement with blood. 



It is manifest from such facts and results that Such of the 

 mammary arteries as supply the milk-glands with blood, 

 are in many cases so over-much expanded and relaxed by 

 engorgement, that the engorged size fix many cows becomes 

 permanent, from the prolonged co72tinuaivce of the engorged 

 condition, and the extreme weakening, and the loss of 

 contractile action and contractive power taking place in 

 the udder-supply artery walls. 



3d. It is evident from several considerations that preg- 

 nant cows require, and have naturally and automatically 

 the power to contract their mammary arteries ; for -Uiis 

 power evidently is necessary to enable them to breed by 

 increasing the placental circulation, which supplies the 

 nourishment to their embryos, and such contraction is a 

 necessity of breeding power. 



If such contraction did not take place instinctively, or 

 from nerve action, by what otlier agency can the blofld be 

 directed to the embryo ? 



The evidence goes to show that the nerve centers which 

 rule blood-supply to the udder, receive impressions of em- 

 bryo hunger, and respond by causing contraction in the 

 mammary arteries, which reduces the rate of milk-forma- 

 tion, and turns the nutritive currents, thus gained, to the 

 supply of the embryo. 



We believe there is no other power but that of contract- 

 ing her arteries, when the reflected impressions of hunger 

 require, that can enable a cow to nourish her embryo, as 

 she naturally does, in time and quantity according to the 

 size and demand of the calf she is breeding. 



Two facts sufficiently show that cows do control so much, 

 at least, of their mammary blood-flow as is necessary to 

 14 



