CHAPTER VII 



THE FEEDING OF MILCH CATTLE 



(i) The formation of milk. 



WHEN the constituents of milk are considered, 

 it is seen that amongst them are some — as, 

 for instance, casein and milk-sugar — which are not 

 found in any other of the tissues or fluids of the 

 body. This fact proves that the milk is not already 

 formed in the juices that flow to the udder, but 

 that it must be separated in the milk glands and 

 pass from them to the cavities of the udder. Milk, 

 therefore, is not a simple excretory product like 

 urine, which is simply filtered from the blood in the 

 kidneys, but it is a substance formed from the 

 fluids of the body by chemical changes in the 

 milk glands. The material which is brought to 

 the mammary gland is utilised first of all to build 

 up certain cells which on completion are wholly 

 or partly destroyed. These products of decom- 

 position are milk, which in this way may be re- 

 garded as a fluid organ. It follows that milk is 

 not directly formed from the blood because of the 



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