DEFINITION OF FOODS. 83 



ture does not become very high and no light is produced. 

 The oxidations which take place in our bodies, are of 

 course slow oxidations; otherwise they would burn us 

 to ashes. 



5. Examples of Slow Oxidation. A good example of a 

 slow oxidation is afforded by the rusting of iron; this is 

 an oxidation; and the rust is iron united with oxygen. 

 This oxidation usually occurs even more slowly than 

 those which take place in our bodies, and heat is given 

 off so slowly that rusting iron does not feel warm 

 when we touch it. You know, too, that iron rusts easily 

 in damp air, and in this respect the oxidation of the iron 

 is like the oxidations which occur inside our bodies, 

 which are moist in every part. 



6. Definition of Foods. Foods include all substances, ex- 

 cept air, taken into the body and serving for any one of three 

 purposes (i) to provide material for its growth or repair, or 

 (2), by their oxidation, to supply it with working power or to 

 keep it warm, or (3) to aid in carrying nourishment from 

 part to part. To the above, we must add that for a sub- 

 stance to be properly a food, neither itself nor anything 

 produced from it inside the body shall be injurious to the 

 structure or action of any organ; otherwise it would be a 

 poison, not a food. 



Most foods serve more than one purpose. Thus meat 

 and bread furnish material for growth and repair, and 

 also supply strength and warmth. Water is found in all 

 the organs, and is a necessary part of them; but it also 



5. Give an example of slow oxidation. In what other respect does 

 the rusting of iron resemble the oxidations which take place in our 

 bodies ? 



6. Define foods. Poisons. What purposes are served by meat 

 and bread ? By water ? Illustrate. 



