92 



HUMAN BIOLOGY 



is found in sweet milk. Crape sugar is found in grapes 

 and honey ; the small grains seen in raisins consist of 



grape sugar ; it can also 

 be prepared artificially 

 from starch. Cane sugar 

 is found in cane, in sap 

 of the maple, and in the 

 sugar beet (Exps. 2, 3). 

 Fats include the fats 

 and oils found in milk, 

 flesh, and plants. A 

 fat, such as tallow, is 

 solid at the ordinary 

 temperature ; while an 

 oil, such as olive oil, is 

 liquid at the same tem- 

 perature. Tallow was 

 oil while it was in the 

 warm body of the ox. Sugar is transformed into fatty 

 tissue as readily as is fatty food itself. 



Proteids are the only foods that contain the tissue- 

 building nitrogen. Protoplasm cannot be formed without 

 nitrogen. We do not often see a pure proteid food, for 

 this food stuff is not so readily separated from foods 

 containing it as are starch, sugar, and fat. AWmmeu, 

 or white-of-egg, is proteid united with four times its 

 weight of water. Pure proteid is also called albumin. 

 Coagulation by heat is one test for proteid (Exp. 4). 

 These are the names of proteids, or albumins, found in 

 several common foods : casein, the curd or cheesy part of 

 milk ; myosin of lean meat ; Jibriji in blood ; legumin 

 in beans and peas ; gluten, or the sticky part of wet flour ; 

 gelatin in bones. Proteid is valuable to the body as fuel 



Fig. 88. — A Tiny Bit of Potato, highly 

 magnified, showing cells filled with grains 

 of starch. Cooking bursts these cells. 



