Artery Relaxation in Practice. 217 



milk, as is frequently done in March, April and May. 

 These cows are only moderate' in their yield, because 

 neither dairymen or non-dairying farmers, as a rule, sell 

 their good cows. The heifers bought up are similar to 

 the cows, the best heifers not being sold. Some of these 

 cows have calved ; others have not. 



When there is grass enough, the factories begin cheese- 

 making. These stranger cows of only moderate yield 

 have formerly been accustomed to poor feed, in scant 

 quantity. As soon as the grass is large enough they are 

 turned to pasture ; and, in addition, many herds are sup- 

 plied with bran, shorts, meal, or other feed, that will in- 

 crease yield rapidly. By the ist of August many of these 

 " new" cows have increased their yield 50 per cent ; some 

 of them double their yield in these three months, or in 

 less time. The size of the udder-supply arteries is enlarged 

 very rapidly, and these artery walls are thinned down 

 so very rapidly, by rapid engorgement with blood, that 

 the thinned walls become relaxed by (7wrstrain, and are 

 kept in a relaxed condition by the maintenance of the en- 

 gorging supply of blood that increases yield so rapidly. 



The degree of artery engorgement and relaxation varies 

 in different cows, from various causes. Late in July, or 

 during August, many of these cows are impregnated, the 

 relaxed condition of their udder-supply arteries not pre- 

 venting impregnation so early after their great increase of 

 feed and blood. The cows eat much more feed, and yield 

 much more milk, and in numbers of them the udder-sup- 

 ply arteries become enlarged as much as 70 to 100 per 

 cent by increase of blood, in only eight to twelve weeks, 

 the average increase in their artery-size being 70 per cent 

 in fourteen months. 



These changes in the size of the udder, and its supply- 

 arteries, and the co-incident thinning and relaxation of the 



15 



