212 Cattle Prohlems. 



that the walls are thinned down twice as rapidly, and as 

 much, when the blood increases to the same extent in four 

 months, compared with the six months rate of increase and 

 thinning ; and three times as rapidly when thinned as 

 much in two months, as happens in some cases, as in six 

 months in other cases or cows. See small Figs. 3, 2, i, 

 lower side diagram Fig. 2. 



In Fig. 3,* read ^yq years instead of five months, as the 

 safe rate of increase (see .table), or 12 per cent yearly ; 

 which doubles yield by the eighth year. This rate of in- 

 crease in blood, does not thin down the artery walls, (see 

 Fig. 3,) such rate of increase being safe, because gradual 

 and slow, but still much more rapid than in most of the 

 best cows in Europe. 



In Fig. 4, a. a., the gradual thickening of the artery 

 walls, according to increased artery-size and augmented 

 blood pressure, is shown ; such increase supplying increased 

 power to bear pressure. The gradual thickening of the 

 artery walls is an important consideration, for of course 

 greater thickness here is required to bear the increased 

 expansive /r^wz/rf arising from, and corresponding to, the 

 increase in quantity and bulk of blood conveyed in and 

 distending the udder-supply arteries, according to any 

 considerable increase in yield, as these arteries — like most 

 other elastic structures — are limited in their power to bear 

 over-strain. 



Heifers may rapidly increase their feed and blood, and 

 artery-size, as shown at r. r., Fig. 5, which may relax their 

 arteries, and cause them to abort. And we are informed 

 by a close observer,'!' '1''^' '^'''^y ^'o abort in as large num- 

 bers of cases as new cows, with which the aborting heifers 

 are usually bought, and brought into special dairy herds 

 previous to their abortments. 



'i" The side lines in the Figs. 3 and 4 should widen a little. 

 •I- Prof. L. B. Arnold. 



