196 ELEMENTS OF PHYSIOLOGY 



337. Composition of Foods. Very few of the articles of 

 food we eat consist of only one of the classes of foodstuffs 

 mentioned ; most foods consist of several foodstuffs com- 

 bined. Oatmeal, for instance, contains starch, a small pro- 

 portion of oil, a large proportion of proteid, some mineral 

 salts, and water. Let us see how the four classes are 

 represented in milk. The part that makes it liquid is 

 water, the sweetness comes from the sugar, the cream rises 

 as oil, and the curd will furnish cheese, which contains 

 casein, a form of proteid. 



338. Experimental Tests of Starch and Proteid. With 

 ten cents' worth of iodine from the drug store the teacher 

 may try the following experiments : Dilute a part of the 

 iodine with water to a light brown color. Make a thin paste 

 by boiling laundry starch in water. Put some of this paste 

 into an ordinary glass and pour a little of the dilute iodine 

 upon it. Notice that the starch turns instantly to a beau- 

 tiful blue color. This is one of the chemical tests for 

 starch, and is called the iodine test. 



339. Put a little piece of lean meat into some of the un- 

 diluted iodine ; the meat turns brown. This is the iodine 

 test for proteid. 



340. Soak some grains of corn, wheat, rye, and other 

 grains for a few hours. Make thin slices across each 

 kernel. Place a slice of each grain in a few drops of 

 dilute iodine in a saucer, and notice which part turns blue. 

 Put slices of each grain into strong iodine, and after they 

 have been acted on for several minutes, rinse off the 

 iodine. Notice which part is blue and which parts are 

 brown. In the grain of corn, for instance, the white part 

 of the kernel turns blue, showing the presence of starch, 

 while the germ and the part around it turn brown, show- 

 ing the presence of proteid. The oil in the corn is mixed 

 with the starch and proteid, and cannot be shown by 

 a simple experiment. If the grain of corn is burned, a 



