FEEDING FOR MILK 67 



making of milk, it now appears that only the free end of the udder 

 •cell is broken down. The contents (protoplasm) of the base of 

 each cell, together with the cell nucleus, is not destroyed but — after 

 the remaining portion of the cell has been changed into milk 

 constituents — the cell is rebuilt.* The constituents of the food of 

 cows are not transformed directly into milk, but are altered and 

 absorbed into the blood and serve only to build the cells of the udder, 

 as they do any other part of the body. 



Moreover, it is probable that the content of the udder cells 

 (protoplasm) is not directly changed into fat, proteids, and milk 

 sugar, but that the cells manufacture these substances out of the 

 materials brought to them by the blood. f There are perhaps some 

 136 million fat globules formed per second in the milch cow's udder, 

 which, it is estimated, would require complete renewal of the en- 

 tire secreting tissue of the udder several times daily — if the udder 

 cells were directly transformed into fat. Fat in the milk is not then 

 due to a breaking down or fatty degeneration of the udder cells, but 

 is a deposit of fat in the cells manufactured from the blood and 

 lymph. 



No one of the separate constituents of milk is directly derived 

 from similar constituents of food. Fat in milk is not derived 

 directly from fat in food, but indirectly is formed from fat, carbo- 

 hydrates and proteids in food. Indirectly, because these substances 

 are greatly altered before and after they reach the udder in the blood. 



Therefore an excess of fat in the food, for instance, will not 

 increase fat in the milk. The kind of food does not influence the 

 composition of milk so long as the food is sufficient in amount and 

 properly proportioned or " balanced " in its constituents to fully 

 nourish and sustain the animal. 



The quality or composition of the milk from any cow depends 

 upon the natural characteristics of the cells of the udder; the 

 quantity of milk depends on the capacity for rapid cell-building 

 and, to a degree, upon the size of the udder. But, although the 



* This destruction is probably confined to but a few of the udder cells, how- 

 ever. It is thought that globulin is thus a product of broken down cells. 



t Fat, casein and milk sugar are the results of glandular activity of the udder 

 cells. 



