FOODS 39 



Alcoholic Fermentation in Diilk. —When yeast is added to milk, 

 the sugar does not readily undergo the alcoholic fermentation. 

 Other somewhat similar fungoid growths are, however, able to 

 produce the change, as in the preparation of koumiss ; the milk 

 sugar is first inverted, that is dextrose and galactose are formed from 

 it (see p. 13), and it is from these sugars that alcohol and carbonic 

 acid originate. 



The Salts of Milk. — The chief salt present is calcium phosphate ; 

 a small quantity of magnesium phosphate is also present. The 

 other salts are chiefly chlorides of sodium and potassium. 



f * EGGS 



r 



Jn this country the eggs of hens and ducks are those particularly 

 selected as foods. The shell is made of calcareous matter, especially 

 calcium carbonate. The luhite is composed of a richly albuminous 

 fluid enclosed in a network of firmer and more fibrous material. The 

 amount of sohds is 13'3 per cent. ; of this 12*2 is proteid in natm-e. 

 The proteids are albumin, vnth smaller quantities of egg-globulin 

 (see p. 26) and ovo-mucoid (p. 28). The remainder is made up of 

 sugar (0"5 per cent.), traces of fats, lecithin and cholesterin, and 0*6 

 per cent, of inorganic salts. The yolk is rich in food materials for 

 the development of the future embryo. In it there are two varieties 

 of yolk-spherules, one kind yellow and opaque (due to admixture 

 with fat and a yellow lipochrome), and the other smaller, transparent 

 and almost colourless : these are proteid in nature, consisting of the 

 nucleo-proteid called vitellin (pp. 29, 30). Small quantities of sugar, 

 lecithin, cholesterin, and inorganic salts are also present. 



The nutritive value of eggs is high, as they are so readily diges- 

 tible ; but the more an egg is cooked the more insoluble do its proteid 

 constituents become. 



MEAT 



This is composed of the muscular and connective (including 

 adipose) tissues of certain animals. The flesh of some animals is 

 not eaten ; in some cases this is a matter of fashion ; some flesh, like 

 that of the carnivora, is stated to have an unpleasant taste ; and in 

 other cases {e.g. the horse) it is more lucrative to use the animal as a 

 beast of burden. 



Meat is the most concentrated and most easily assimilable of 

 ' nitrogenous foods. It is our chief source of nitrogen. Its chief sohd 

 constituent is proteid, and the principle proteid is myosin. In addi- 

 )n to the extractives and salts contained in muscle, there is always 



