CHEMISTRY AND FOOD 251 



described from the chemical point of view as one which 

 furnishes: (i) sufficient amounts of digestible material to 

 yield when burned in the body the necessary number of 

 calories of energy; (2) enough protein of suitable sorts; 

 (3) adequate amounts and suitable proportions of a 

 number of mineral or inorganic elements (the ash con- 

 stituents of the food); (4) enough of each of at least 

 three kinds of vitamins. 



If a mechanical analogy helps, one may compare the 

 body and its food to a gasolene engine and its require- 

 ments. The digestible organic foodstuffs such as fats, 

 sugars, and starches correspond to the fuel for the engine; 

 the proteins and some of the mineral matters to the 

 materials of which the motor is made; other mineral 

 matters to the lubricant; and the vitamins to the igni- 

 tion sparks whose own energy is insignificant but with- 

 out which the engine cannot run, however fine the ma- 

 terials of which it is built or however abundant and 

 appropriate the supplies of fuel and of lubricant. 



The efficiency with which economy in the use of food 

 can be combined with entire adequacy of nutrition is 

 chiefly dependent upon the extent to which we can state 

 the various esssentials of an adequate diet in quantita- 

 tive terms. Here in the most practical manner imagin- 

 able the exact science of the research laboratory in food 

 chemistry comes directly into the service of human nu^ 

 trition. How best to spend a dollar in the purchase of 

 food for a family, or how best to divide the money which 

 is to be spent for food is a problem more often met 

 than faced and one which may well serve to put into 

 practical use whatever knowledge of food values and 



