Section IV.— DAIRY PRODUCTS 



Mii,K is composed of about Sy per cent, water, about 

 3'8 per cent, of fat, and 9*0 per cent, of other solids. The 

 fat resembles ordinary animal fat, excepting that it con- 

 tains rather higher proportions of butyrin and other fats 

 containing the lower fatty acids. The chief nitrogenous 

 material is casein, or caseinogen, which is characterized 

 by being precipitated in acid solutions. Milk also con- 

 tains a small quantity of alTjumen, which is precipitable 

 by heat. Milk sugar is the only form of sugar present 

 in milk, and on hydrolysis or digestion gives glucose 

 and galactose. The mineral matter is fairly constant at 

 0*75 per cent, of which calcium phosphate, sodium chloride, 

 and potassium chloride constitute the major part. Milk 

 is produced directly by the breaking-down process of the 

 tissues in the glands, and is not dependent upon the composi- 

 tion of the food supplied, but is maintained in molecular 

 equilibrium with the blood. Consequently, the molecular 

 concentration of the soluble portions is fairly constant, 

 but a deficiency of milk sugar may be replaced by an increase 

 in the amount of soluble salts. The freezing-point of milk 

 is in consequence regular. There is a constant relationship 

 between the specific gravity and the materials of which the 

 milk is composed. This has been brought out by many 

 authors (see Bibliography), and may be very simply ex- 

 pressed by the formula that the non-fatty solids = J of the 

 gravity 4- ! of the fat -f- 0*14, the fat being represented as 

 percentages, and the gravity being the final figures of the 

 specific gravity, after removing the I'o which is constant in 

 all milks. The composition of the milk will vary according 

 to many causes : — 



