Milk and Its Products. 269 



The composition of the milk of a single species is by no means- 

 similar to that of another, although the constituents forming it, 

 so far as they have been investigated, are of a similar nature. 



The constituents of milk may be divided into the following 

 classes: water, fats, proteins, sugar and ash. The water of 

 milk constitutes from 85 to 88 per cent and needs no discussion. 



Fats of milk. The fats resemble in chemical constitution the 

 animal and vegetable oils and fats already discussed; that is, 



The milk chambers or alveoli of an udder; A and B, secreting alveoli; 

 C and D, non-secreting alveoli; E, alveolus, which has discharged 

 its milk (cells appear flattened). 



they consist of compounds of fatty acids and glycerine. They 

 differ from animal fats chiefly in containing acid radicals of low 

 molecular weight, in addition to the heavy acids, such as oleic, 

 stearic, and palmitic, which are the principal fatty acids in the 

 fats of animal tissue. Butter fat consists of the glycerides of 

 at least 9 fatty acids. The lowest member of the group is butyric 

 acid, the highest is stearic acid. Oleic acid belongs to another 



