Abortion in Coivs. 203 



arteries, just previous to and after the birth of the calf; 

 and milk in the udder is held up or allowed to flow by 

 contracting or relaxing elastic bands around the teat 

 sinuses. Suspend the question of control by nerve action 

 briefly, and the fact of nutrient blood-flow to the udder, 

 and the positive necessity for increasing its flow to the 

 embryo still exists ; for there is no other source than the 

 mammary blood* from which to increase embryo nutrition 

 in pregnant cows. So, contraction in the milk-glands, 

 and in the size of the udder-supply arteries, is a natural 

 necessity to supply an increase of blood, through the 

 placental vessels, to enlarge and continue embryo growth 

 till completed. 



But the power of contracting their udder-supply arteries 

 is either suspended or destroyed in nearly all aborting 

 cows, as in nearly all the abortions from evident starva- 

 tion the embryos are dead previous to abortment. 



Breeding power is necessary to supply a succession of 

 cows, and constant increase in size is a law of embryo life 

 till parturition, and in the animal afterward, till full size 

 is formed. Even the few dwarfed embryos that are abort- 

 ed alive, making some little increase in size by growth. 



But the relaxation of the udder-supply arteries at an ex- 

 cessive and fixed size, and their remaining at a fixed and 

 uncontracting size, as uncontracting tubes, prevents any 

 increase of blood to the embryo, thereby arresting de- 

 velopment, preventing any further increase in size, and so 

 abruptly and entirely arresting growth and starving the 

 embryos to death, from the deficient blood supply, result- 

 ing from loss of contractile power in the udder-supply 

 artery walls. 



The arrest of growth arrests the demand for blood, and 



*A8 the mammary blood certainly has no innate power to change its 

 course, some contracting force ia a necessity, which is supplied by contract- 

 ile power under nerve inliuence, determining the direction and extent of 

 the mammary blood-ilow, so far asmay be necessary to embryo nutrition, 



