74 VETERINARY STUDIES 



in that it contains the colostrum cells, a few oil globules, much 

 albumin, and but little casein, fat or sugar. It has a mild, 

 cathartic effect on the young animals. 



Milk is a complex alkaline fluid with a specific gravity of 

 1018 to 1040. It is composed of oil globules suspended in milk 

 plasma, and is therefore an emulsion. Milk globules consist 

 almost entirely of fat. They are from .0004 to .0012 of an inch 

 in diameter. The plasma consists of water, with casein, sugar, 

 salt, albumin, and whatever else may be in solution in the water. 



Milk production. — The production of the casein, sugar, fat, 

 etc., is a manufacturing process, not mere filtration; for there 

 is no casein or milk sugar in the blood, and but very little fat. 

 Secreting cells take certain elements from the blood and lymph 

 and put them together to make the milk ingredients. 



The formation of milk consists of two processes; one of these 

 is gland secretion, e.g., of the casein and milk sugar, by the lin- 

 ing epithelial cells. In the other process, the fat or cream is 

 formed as tiny droplets in the ends of these cells. The end of 

 the cell may either cut off or rupture, freeing the fat droplet in 

 the cavity of the alveolus. The cell is then repaired and forms 

 the next droplet, of fat. 



Practical application. — It is important to remember that the 

 two lateral halves of the cow's udder are completely separated 

 by a strong partition, but that the front and back quarters in 

 each half are not so separated. This is important in connection 

 with garget and other diseases of the udder. 



Pressure of milk within the udder checks secretion ; removal 

 of this pressure stimulates or at least permits secretion; hence 

 the importance of complete milking. 



The quantity and quality of milk depends, first of all, upon 

 hereditary peculiarities of the individual cow; after this it de- 

 pends upon food and thoroughness of digestion and absorption. 

 They depend, also, upon the length of time the cow has been 

 milking, the length of time she has been carrying her calf, the 

 condition of her nervous system, and, to a very great extent, 

 upon the quantity and composition of blood passing through the 

 udder. 



The composition of blood for milk production depends upon 

 the amount and character of food received, and upon the thor- 

 oughness of digestion and absorption from intestines into the 

 blood. 



