CHAPTER XLI 

 THE CHIEF FOODSTUFFS 



IT is necessary to consider a few of the commoner foodstuffs in 

 more detail. 



Milk. Cow's milk is a staple article of diet for persons of all ages. 

 It is to be noted that milk is relatively a watery, and therefore not a 

 cheap, food. Fresh cow's milk is amphoteric in reaction, with a 

 specific gravity of 1028 to 1034. When skimmed, the specific gravity 

 rises to 1033 to 1037. A little water added will again reduce the 

 specific gravity, and a little colouring matter will help to cover up 

 the fraud. Milk contains all the necessary foodstuffs proteins, fat, 

 lipoids, carbohydrate, water, and salts. The chief protein is case'n- 

 ogen, a phospho-protein, notable for its high content in the ringed 

 amino acids tyrosin and tryptophane. A certain amount of coagu- 

 lable protein -lactalbumiri is also present. Caseinogen is clotted by 

 rennet. When this takes place outside the body, " junket " is formed. 



Caseinogen is easily precipitated from solution by acid. When 

 milk goes sour on standing, lactic acid is formed as the result of the 

 action of a bacillus B. lactis upon the sugar contained in milk. 

 The lactic acid so formed precipitates the caseinogen as the " curds," 

 leaving a clear fluid the " whey." The term " whey " is often given 

 to what is left after caseinogen has been removed by any means. 

 When milk is clotted, a clear fluid exudes after a time " rennet 

 whey." If caseinogen be precipitated by acid, neutral salts or 

 alcohol, " acid," " salt," or ' : alcoholic " whey is obtained. Some wheys 

 e.g., rennet, acid contain lactalbumin; others do not, the albumin 

 being removed with the caseinogen e.g., alcoholic whev. 



The fats of milk are carried down with the caseinogen. Olein 

 forms the chief fat (43 per cent.); palmitin (33 per cent.) and stearin 

 (17 per cent.) are also present, together with 7 par cent, of fats of the 

 volatile fatty acids butyrin, caproin, and caprylin. It is this con- 

 tent of volatile fatty acids which aids to distinguish butter from 

 margarine. The fats occur in the form of fine droplets, each drop 

 of the emulsion b?ing surrounded with a fine film of caseinogen. 



In the whey are contained the sugar lactose and the salts. The 

 chief salt is calcium phosphate; the phosphate of magnesium and 

 the chlorides of sodium and potassium are also present. Milk con- 

 tains but little iron. The milk of different animals varies in the 

 content of the chief constituents. The differences between cow's 

 and human milk are discussed elsewhere (see p. 537). The composition 



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