THE COW IN HEALTH AND DISEASE 113 



of these small acini or alveoli of an animal 

 that has never been pregnant, we will find that 

 the cells lining it, and also the small acini, are 

 much fewer in number than they are in an 

 animal that is milking; the cells are also of a 

 very slow growing kind and may be so nu- 

 merous as to fill up this small cavity. When 

 the heifer gets with calf these small acini be- 

 come greater in number and cells that fill 

 them are discharged with the first milk which 

 is known as colostrum. If examination is 

 made before the udder has been milked, the 

 cells lining these small acini will be apparently 

 flat; but if the udder is milked out the cells 

 will be long with a constricted base and com- 

 ing free from the base are discharged as the 

 fat of the milk. They leave behind them the 

 parent cell from which other cells grov/. This 

 process, continued, produces the fat content 

 of our milk. No fat consumed by an animal, 

 but a protein diet influences the fat content of 

 milk. It is needless to say that these exam- 

 inations must be made with a microscope. 



The fluid part of milk is composed of water, 

 proteins, salts, and sugar. These are taken 

 from the lymph that flows through the udder, 

 by the cells lining the small alveoli and lo- 

 bules. The lymph is made up largely from 

 the blood, being the fluid part of it, with nour- 

 ishment from the digested food eaten by the 

 animal. The blood in flowing through the 

 arteries and capillaries finally arrives at ves- 



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