WASTE AND REPAIR FOODS 83 



Organic foods may be subdivided into animal and vegetable 

 foods ; and each of these again into nitrogenous and non -nitro- 

 genous. 



Among the animal nitrogenous foods may be mentioned 



(1) Albumen. This substance may be obtained from white of 

 egg, of which it forms about 20 per cent. It is a clear and trans- 

 parent liquid when fresh, but coagulates, when heated, into a white 

 opaque solid. 



(2) Casein (Lat. caseus, cheese). This compound exists largely 

 in milk, from which it may be separated in a solid form by the 

 addition of an acid. This is illustrated in the making of 

 cheese ; the milk is separated into curds and whey by the ad- 

 dition of rennet, and the curd from which the cheese is made 

 contains the casein. 



(3) Fibrin (Lat. fibra, a fibre). Fibrin exists in blood. 



(4) Myosin (Gr. mus, a muscle). This is an important con- 

 stituent of the juice of muscles. It is converted into syntonin by 

 the addition of an acid. 



The above four nitrogenous substances all closely resemble 

 each other in chemical composition, and are all termed albumi- 

 noids. 



(5) Gelatine. This may be obtained from bones by boiling. 

 It swells considerably in cold water, but does not dissolve. It is 

 soluble in hot water, and when the solution cools it forms a 'jelly.' 

 The different kinds of glue are varieties of gelatine. 



The chief vegetable nitrogenous foods are : 



(1) Gluten. This substance exists in all cereal grains. It 

 forms about i o per cent, of wheat flour, from which it may be 

 obtained as follows : Tie a little wheat flour in a calico bag, and 

 well knead it in a vessel of water. A substance passes through 

 the interstices of the calico which gives a milky appearance to the 

 water. This substance is starch. After removing as much as 

 possible of the starch in this manner, the contents of the bag will 

 consist of a very sticky substance, which may be drawn out into 

 threads. This is gluten. Gluten so closely resembles fibrin that 

 it is sometimes termed vegetable fibrin. 



(2) Legumen. Legumen exists largely in all kinds of peas 

 and beans, and other seeds. 



The principal non-nitrogenous foods are : 



(i) Starch. This is a vegetable substance which exists largely 

 in various parts of plants. A method of separating it from flour has 

 just been described ; it may also be obtained in large quantities 

 from potatoes, rice, arrowroot, &c. It is insoluble in cold water, 

 but dissolves slightly in hot water, forming a kind of jelly on cool- 

 ing. 



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