CHAPTER XV. 

 MILK AND MILK PRODUCTS; 



MILK is the natural secretion of the special glands of a female, intended 

 for the nourishment of the new-born. The mammary glands are, in 

 general, only developed in the female and are active im producing their 

 secretion for a certain period after parturition. In certain abnormal' 

 instances, however, males have been known to produce milk, but such- 

 cases are rare. 



The milks of different animals differ considerably, both in the con- 

 stituents present and in the proportions of the constituents.. 



The milk of the cow is the most important and Unas- been studded! 

 in greatest detail. 



The constituents of milk are usually divided into 



Water, 



Fat, 



Albuminoids, 



Sugar, 



Ash. 



A short account of the chemical nature of these constituents (ex- 

 cluding water) may be here given. 



Fat. The fat present in milk resembles in general constitution the 

 true animal and vegetable fats already described (see p. 197). Like 

 them it consists of a mixture or compound of the glyceryl salts of 

 fatty acids. 



It differs, however, from other oily substances in the character of 

 the fatty acids present. 



In milk fat, considerable quantities of acid radicals of low molecular 

 weight are present, besides the stearic, oleic and other heavy acids 

 found in other fats. 



In common with most natural fats, it is probably a mixture, though 

 whether each acid radical is present as a distinct glyceryl salt or 

 whether two or three different acid radicals may be attached to the 

 same glyceryl group is uncertain. The latter hypothesis is probably 

 more correct. 



The proportions of the various fatty acids found in butter are sub- 

 ject to considerable variation according to the food ; they are said also^ 

 to vary with the season of the year. The fat of milk given by cows, 



(312) 



