380 GENERAL SCIENCE 



bodies is in the oxidation of the fuel or food we eat. All 

 the various manifestations of energy, such as heat and 

 action in the body, have the same source. Since some 

 parts of the body are always in action and since the body 

 must be kept at constant temperature, there must always 

 be a supply of food present in the body to supply this 

 energy. 



Measurement of Food Values. By careful experiments 

 it has been found that the work equal to lifting 427 grams 

 a distance of one meter will produce a calorie of heat or 

 enough heat to raise the temperature of one gram of 

 water one degree Centigrade. Since this relation between 

 heat energy and work exists, it is usual to give the values 

 of different foods in terms of the calories they are capable 

 of producing. Fuel values of foods are usually given 

 in large calories, or a calorie equal to 1000 of the small 

 calories mentioned above and written Calories. Food 

 is actually fuel for the human organism, and the con- 

 sideration of food on this rational and intelligible plan 

 has furnished a logical basis for a constructive study of 

 practical dietetics and the nutrition of the individual. 

 There are some essential food factors whose value 

 cannot be accurately shown in terms of calories, but 

 they are like the lubricants for a great machine ; they 

 are essential, but they do not furnish the energy to run 

 the machine. 



Source of Food. Agriculture is the great source of 

 food supply. The rapidly developing transportation 

 facilities have made it possible to utilize profitably an 

 increasing amount of the earth's surface for agriculture. 

 A hundred years ago it would have been a waste of energy 

 to raise an enormous crop of wheat in the inland portions 

 of the middle West, since there was no adequate way to 



