CHAPTER XIX 



MILK AND DAIRY PRODUCTS 



The most valuable products of the animal are milk and its 

 derivatives. Most of these materials are used as food for 

 man. Milk in particular, as Hawk says, is the most satis- 

 factory individual food material elaborated by nature, in 

 that it contains protein, fat, and carbohydrate in addition 

 to mineral matter, all combined in such form and proportion 

 as to make it palatable, nourishing, and easily digested. 

 The following discussion applies solely to milk from cows, 

 since that has been most studied and since milk from other 

 animals differs from it only in the proportion of the various 

 constituents. 



243. Physical Appearance. — Milk is a white, opaque 

 liquid, the specific gravity of which is about 1.03, with a 

 slightly sweet, pleasing taste, and a freezing point of — 0.56° C. 

 Its color is due to minute particles of fat in suspension and 

 also to the presence of a protein, caseinogen, in pseudo- 

 solution. 



244. Chemical Composition. — Milk is composed of a clear, 

 aqueous solution of carbohydrate, inorganic salts, and 

 protein, in which are suspended fat globules, calcium phos- 

 phate, and a protein in semi-suspension. The average com- 

 position is as follows: Water, 87.75 per cent.; fat, 3.4 per 

 cent.; protein, 3.5 per cent.; carbohydrate, 4.6 per cent.; 

 and inorganic salts, 0.75 per cent. 



(a) Carbohydrate. — Lactose is the only carbohydrate 

 present in milk sugar. It is an aldose sugar whose formula is 

 C12H22O11, graphically: 



