THE ANIMAL AS A MOTOR. 



71 



(4) Produce muscular and intellectual energy for the work it has to 

 do. 



The body is built up and its wastes are repaired by the nutrients. 

 The nutrients also serve as fuel to warm the body and supply it with 

 strength. 



A growing child or young animal requires much 

 muscle and nerve-making material, and the proportions 

 of the several elements in the food are more nearly 

 those of the body itself than in the case of the adult. 

 The adult, when doing little work, requires little food, 

 and that mainly of the kinds which are required to 

 supply heat and to compensate the slight wastes of 

 tissue then occurring ; while the working system, and 

 particularly if hard worked, demands considerable 

 quantities of combustible, heat-producing food. Simi- 

 lar differences of dietary are required, as the climate 

 compels the development of more or less of caloric to 

 preserve the temperature of the body, which at above 

 104" Fahr., or a little below 98", fails to meet the 

 requirements of hfe. 



According to Dr. Letheby, the working-power of the 

 human body may be taken as follows : 



( are consumed for fuel. 

 The carbohydrates j are changed into fat. 



of food \ are consumed for fuel. 



forms the nitrogenous basis of blood, muscle, 



sinew, bone, skin, etc. 

 is changed into fats and carbohydrates. 

 is consumed for fuel. 



* Letheby on Food, p. 96. 



