FOOD AND NUTRITION 259 



stopper, and shake. If the red color disappears in three 

 minutes or less, the air is unfit to breathe. 



The following table is taken from book No. 1905. 



" The percentage of carbon dioxide may be estimated from 

 the time which it takes to decolorize the phenolphthalein as 

 follows : 



TIME PER CENT VOLUME 



Minutes Carbon Dioxide 



1J 1618 



If 1318 



1| .1279 



3i 07716 



4i 05142 



5 0434 



7| 0351" 



6. See Experiment 48 for another test for carbon dioxide. 



191. FOOD AND NUTRITION 



We learned, in connection with plants, that food was nec- 

 essary to promote growth, and to supply the wastes which are 

 going on all the time. With animals, food is even more nec- 

 essary, for, on account of their great activity, they require it in 

 much larger quantities. 



Food serves three purposes: to supply energy, fat, and 

 muscle-forming materials. The warmth of the body is pro- 

 duced by slow oxidation of the carbohydrates contained in 

 some foods, as well as by fats. Fats, in the body, serve as 

 storehouses of food which can be utilized if the food supply is 

 lacking. Proteids supply material for the production of new 

 cells. Other things being equal, the moderately fat person 

 has a better chance to survive a period of starvation than a 

 thin person. 



