CHAPTER XVIII 

 MILK 



MILK is the most satisfactory individual food material elaborated 

 by nature. It contains the three nutrients, protein, fat, and carbohy- 

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

 acceptable dietary constituent. Its dietary value is also enhanced by 

 the presence of the three mtamines, Fat-soluble A, Water-soluble B 

 and Water-soluble C. Milk would be an ideal food were it not for its 

 low iron content and for a slight deficiency in water-soluble B. 1 Milk 

 is a specific product of the secretory activity of the mammary gland. 

 It contains, as the principal solids, olein, palmitin, stearin, butyrin, 

 casein, lactalbumin, lacto- globulin, lactose, phosphates of c-alcium, potas- 

 sium and magnesium, citrates of sodium and potassium, chloride of 

 calcium, iron and mtamines. It also contains at least traces of lecithin, 

 cholesterol, urea, creatine, creatinine, and the^tri-glycerides of caproic, 

 lauric and myristic acids. The calcium phosphate of milk is the 

 neutral calcium phosphate, CaHP0 4 . 2 According to Osborne and 

 Wakeman 3 milk contains two phosphatides, one being probably stearyl- 

 oleyl-lecithin. These same investigators 4 have also shown milk to 

 contain an alcohol-soluble protein. 



The presence of the vitamine Fat-soluble A in butter fat was first 

 demonstrated by McCollum and DaVis and by Osborne & Mendel. 5 

 For discussion of vitamines, see Experiment I, page 580.) 



Summer milk has a higher vitamine content than winter milk. 6 



The preparation of milk in the form of a powder has become an 

 important industry. 



By passing milk through a special form of earthenware filter Van 

 Slyke and Bosworth 7 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 



Osborne and Mendel: Jour. Biol. Chem., 41, 515, 1920. 



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



3 Osborne and Wakeman: Jour. Biol. Chem., 21, 539, 1915; 28, i, 1916. /^ 



4 Osborne and Wakeman: Jour. Biol. Chem., 33, 243, 1918. 



5 McCollum and Davis: Jour. Biol. Chem., 15, 167, 1913; Osborne and Mendel: ibid., 

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



6 Hart, Steenbock and Ellis: Jour. Biol. Chem., 42, 383, 1920. Hess, Unger and Supplee: 

 Jour. Biol. Chem., 45, 229, 1920. Dutcher, Kennedy and Eckles: Science, 52, December 

 17, 1920. 



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



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