CHAPTER XIII 



MILK PRODUCTION 



i. THE PHYSIOLOGY OF MILK PRODUCTION 



546. Components of milk. In addition to water, milk 

 contains representatives of the four great groups of nutrients, 

 viz., proteins, fats, carbohydrates and ash. 



Proteins. The principal protein of milk is casein, a sub- 

 stance belonging to the group of phosphoproteins (65). This 

 protein is peculiar to milk, not being found elsewhere in the 

 body. 



In addition to casein, milk contains also a lact-albumin and a 

 paraglobulin in small amounts. Their presence may be demon- 

 strated by precipitating the casein by means of acid and heating 

 the nitrate. Traces of peptones, possibly due to the presence 

 of a proteolytic enzym, are also found in milk. 



According to Konig, the casein content of milk has been 

 observed to vary from 1.79 per cent to 4.23 per cent and that 

 of the other proteins from 0.25 per cent to 1.44 per cent. 



Fats. Fats occur in milk in the form of microscopic glob- 

 ules varying greatly in size and held in suspension in the col- 

 loidal solution of casein. In cow's milk the diameter of these 

 fat globules may be stated in a general way to range from 

 0.0016 to o.oi millimeter and in a single cubic centimeter of 

 average milk their number runs into the millions. The fat 

 globules were formerly described as surrounded by a membrane 

 of a protein nature, but the supposed membrane is now re- 

 garded as simply a condensation of the protein of the milk, due 

 to surface tension. 



Milk fat, like other animal fats, is a mixture of a number of 

 simple fats or triglycerids. As compared with body fats, the 

 fat of milk is relatively rich in olein and consequently has a 

 relatively low melting point. It is especially distinguished from 



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