426 FOODS 



but they are not generally classed as foods. In leaves 

 then and in leaves only are the lifeless (inorganic) sub- 

 stances of the earth combined into substances that will 

 support life (organic compounds) . The factories of nature 

 are open to man, and he knows fairly well what these fac- 

 tories produce. But how the compounds are produced 

 either in the plant or in the animal and how the active 

 material of the living cells called protoplasm does its work 

 are mysteries to him. By careful study, however, man 

 has learned a great deal as to foods necessary to the growth 

 and health of the human body. 



Necessary Foods. Experiment 139. Place in different test 

 tubes small amounts of (1) corn starch, (2) grape sugar, (3) scrap- 

 ings from a raw potato, (4) flour, and (5) the white of an egg. 

 Pour in a little water and shake thoroughly. Drop into each 

 tube a few drops of the iodine solution prepared in Experiment 120. 



Experiment 140. Place in test tubes small quantities of (1) the 

 white of a hard-boiled egg, (2) tallow or lard, (3) grape sugar, and 

 (4) any other food which may be handy. Pour a little concen- 

 trated nitric acid into each tube and allow to stand for a minute. 

 Be careful not to get the nitric acid on the clothes or hands. Pour 

 the acid out into a slop jar and wash the substances with a little 

 water. Pour off the wash water and pour on a little strong am- 

 monia. If the substances turn a yellow or orange color, proteins 

 are present. Which substances contain proteins? 



Experiment 141. Gasoline vapor is very inflammable ; be sure 

 in this experiment that there is no flame in the room. Place about 

 a spoonful of (1) both the white and the yellow of an egg, (2) flax- 

 seed meal, (3) yellow corn meal, (4) white flour, and (5) other 

 foods it is desired to test in separate evaporating dishes or beakers 

 near an open window. Pour on these more than enough gasoline 

 to cover them, and stir thoroughly. Cover the evaporating 

 dishes and allow to stand for ten or fifteen minutes. Pour the 

 gasoline off into a beaker and set the beaker outside the window 

 until the gasoline has evaporated. If there is anything left it 



