Milking and Breeding. 257 



undistended, and remains of small size. But by long con- 

 tinued storage of a twelve-hour yield, the natural small size 

 of the udder has been greatly expanded and enlarged. 

 And since the commercial demand for milk products led 

 to the increased demand for milk, special dairymen have 

 largely increased the size of the udder, by increasing the 

 yield of their cows. This illustrates the expansive effect 

 of milk, and its pressure on the size of the udder, as a 

 store tank or reservoir. 



Now as to enlargement in the hind quarters : The blood 

 is continuously forming by digestion, being colored and 

 completed vitally by breathing. The rate of blood pro- 

 duction varies with the rates of breathing and nutrition ; 

 and blood production constantly continues in a less or 

 greater degree, the tissues of the cow receiving their nu- 

 tritive supply continually. But the blood that supplies 

 the udder is not constantly in use, and flowing like that 

 which nourishes the tissues of the cow. The milk-glands 

 receive blood and form milk at certain seasons only. After 

 calving, a large increase of blood takes place in the udder- 

 supply arteries from which the milk-glands regularly re- 

 ceive their supplies. The milk-glands admit the milk-form- 

 ing blood till they are full ; there is then a back-setting 

 process, by which the arteries are further distended in size. 

 They are also increased in length to some extent, and in 

 the extent of their convolutions and ramifications ; and 

 probably also in the number of their smaller branches. In 

 this way the concurring effect from increase of blood and 

 milk storage in the udder, is to increase the tubular 

 or containing capacity of the udder-supply arteries as much 

 beyond the natural, or previous size, as the yield of milk 

 and the size of the milk-glands and udder are increased ; 

 the enlarged supply of blood for forming milk necessarily 

 requiring an equal increase in the artery space, which it 

 fills and occupies, previous to passing to the milk-glands. 



