JUDGING LIVE STOCK. 115 



tures, separated by a strong fibrous band running longitudi- 

 nally of the body. These two large masses of glandular 

 structures are again subdivided, though not absolutely, and 

 from each of the quarters so formed a teat extends. 



The exact structure of the udder is perhaps easiest under 

 stood by viewing it from an external standpoint. The teal 

 has a small canal leading up through it; a small muscle 

 (sphincter) controls the flow from this canal; at the uppei 

 end of the teat a cavity, variable in size, is found. Thia 

 serves to hold milk as it is secreted, and is known as the 

 milk reservoir; from it, large ducts branch to all parts ol 

 the udder. These branches constantly subdivide, and each 

 one finally enters one of the glandular structures referred to 

 above; within this glandular structure it divides into in 

 numerable branches which have as lateral or terminal en 

 largements other small glandular structures known as al- 

 veoli. The alveoli are lined, internally, by epithelial cells, 

 which are believed to play the most important part in the 

 secretion of the milk. The structure of the udder may be 

 likened to a great river system in which the alveoli are 

 springs, their capillaries small creeks, the junction of these 

 into one large duct leading from each glandular structure, 

 as the junction of all the creeks of some river basin into 

 one river, and the large ducts flow to the milk reservoirs 

 as large rivers flow to a lake. 



Such, in brief, is the structure of the udder; and careful 

 experiments have established two facts: 



1st. The amount of milk secreted increases with the flow 

 of blood through the udder. 



2d. This flow of blood is controlled, in a large part, bj 

 the nervous system; and while the nerves act reflexly foi 

 the most part, they are under the control of the cow when 

 she sees fit. This explains the "holding up of the milk" by 

 cows when excited or irritated. 



The old idea concerning the udder was that it merelj 

 acted as a filter for the blood; but chemical analysis has 

 shown that this is impossible, and that certain manufacturing 

 processes go on in the udder. The precise nature of these 

 is not yet definitely known; but it appears that the casein, 

 fat, milk sugar, albuminoids, and part of the ash of milk are 

 manufactured in the udder from the constituents of the 

 Hood; and that the alveoli of the gland-lobules are of chief 



