202 Cattle Problems. 



form embryo growth, and thus make breeding possible, 

 the last-named fact being indispensable and natural : — 

 - ist. Cows necessarily supply their embryos with blood 

 - nutriment, when they feel the embryo hunger through the 

 combined nerves of both. 



2d. They naturally increase the blood supply to the em- 

 bryo according to its increase in size and constantly in- 

 creasing demand, to form the equally constant enlarge- 

 ment — which is growth — till pregnancy terminates. 



It is also true that some cows starve their own tissues 

 more than they should, from strong nerve impressions that 

 it is necessary to nourish their embryos, which is an evi- 

 dence that they direct the mammary blood flow by nerve 

 action. 



A large majority of cows increase the blood supply to 

 the embryo by contracting the udder-supply arteries ; in 

 this way increasing the flow of blood to the embryo by re- 

 ducing the supply that is flowing to the milk-glands. 



By contracting the udder-supply arteries, they increasing- 

 ly nourish their embryos, and at the same time reduce 

 their milk-yield, until the enlarging growth of the embryo 

 and the increasing contraction of the milk glands and 

 their supply arteries, entirely dries up the milk-yield, by 

 contractively reducing and at length stopping the flow of 

 blood to the milk-glands, or udder. 



The propulsive force of contraction, alternately with ex- 

 pansion, propels the artery blood generally. But it is in- 

 conceivable that the mammary circulation could be re- 

 duced in one direction, and increased in a different direc- 

 tion, as it evidently is, in quantity according to the size 

 and needs of the embryo, otherwise than by the cow con- 

 trolling the blood flow that supplies the udder, by con- 

 tracting the udder-supply arteries. Contractile power 

 propels the mammary blood towards the udder, in the 

 season of its use by the ralf, through the udder-supply 



