Formation of Milk. 43 



fresh, and, if it must be kept, to preserve it in pure air 

 only ; or keep it where it cannot be contaminated by con- 

 tact with impurities of any sort. 



The condition of the udder sack as to elasticity, is to a 

 considerable extent an index of the condition of the udder 

 supply arteries. If the udder has become flimsy and 

 inelastic from over-strain and relaxation from excess of 

 milk yield, the arteries supplying the milk glands are, in 

 some cases, liable to certain degrees of over-strain and 

 relaxation from the corresponding increase of blood. 

 The milk glands themselves, as well as the udder skin, 

 are liable to undue or over-rapid expansion, over-strain, 

 and relaxation, from over-rapid increase in blood and milk, 

 when yield is more rapidly augmented than the glands 

 can be strengthened by nutrition in their various parts ; 

 or the skin of the udder can be thickened by nutrition 

 from the general circulation. Uncontracting udders are 

 difficult to dry, as dairymen are well aware ; for this 

 result — udder relaxation, and prolonged duration of yield 

 — has long been a perplexing problem, while the failure of 

 many cows, so affected, to breed, has equally perplexed 

 their owners, as we have observed, in various localities 

 and States ; both points being specially considered in other 

 chapters of this work. 



