CHAPTER XVII 

 MILK 



MILK is the most satisfactory individual food material elaborated by 

 nature. It contains the three nutrients, protein, fat, and carbohydrate 

 and inorganic salts in such proportion as to render it a very acceptable 

 dietary constituent. It is a specific product of the secretory activity of 

 the mammary gland. It contains, as the principal solids, oiein, 

 palmitin, stearin, butyrin, casein, lact-albumin, lacto-globulin, lactose, 

 phosphates of calcium, potassium and magnesium, citrates of sodium 

 and potassium and chloride of calcium. The calcium phosphate of 

 milk is the neutral calcium phosphate, CaHPO 4 . 1 Milk also contains 

 some iron but not enough for the needs of the body if milk is the only 

 source of the iron. It also contains at least traces of lecithin, cholesterol, 

 urea, creatine, creatinine, and the tri-glycerides of caproic, lauric, and 

 myristic acids. According to Osborne and Wakeman 2 milk contains 

 two phosphatides, one being probably stearyl-oleyl-lecithin. 



Recent investigations indicate the presence in milk of some sub- 

 stance or substances of unknown character which are of great nutritional 

 importance. The presence of a growth- promoting substance (vitamine) 

 in butter fat has been demonstrated by McCollom and Davis and by 

 Osborne and Mendel. 3 



By passing milk through a special form of earthenware filter Van 

 Slyke and Bos worth 4 have obtained a separation of the constituents in 

 milk which are in true solution from those insoluble in water or 

 in suspension. The soluble constituents and the water constitute 

 the milk serum. They suggest the following classification of milk 

 constituents: 



CONSTITUENTS OF MILK 



i h i 



In true solution in milk Partly in solution and Entirely in suspension 



serum. partly in suspension or or colloidal solution. 



colloidal solution. 



1. Lactose. i. Albumin. i. Fat. 



2. Citric acid. 2. Inorganic phosphate. 2. Casein. 



3. Potassium. 3. Calcium. 



4. Sodium. 5. Magnesium. 



5. Chlorine. 



1 Van Slyke and Bosworth: Jour. Biol. Chem., 20, 135, 1915. 



2 Osborne and Wakeman: Jour. Biol. Chem., 21, 539, 1915. 



3 McCollom and Davis: Jour. Biol. Chem., 15, 167, 1913; Osborne and Mendel: ibid, 

 15, 311, 1913; 24, 37, 1916 (previous references cited in this article). 

 4 Van Slyke and Bosworth: Jour. Biol. Chem., 20, 135, 1915. 



