CHAPTER XII 

 ENERGY SUPPLY OF THE BODY 



IF one stops taking food, it becomes difficult after a time 

 for him to move about and to keep warm. These results 

 show that food has some relation to the energy of the body, 

 for motion and heat are forms of energy. The relation of 

 oxygen to the supply of energy has already been discussed 

 (Chapter VIII). We are now to inquire more fully into 

 the energy supply of the body, and to consider those condi- 

 tions which make necessary the introduction of both food 

 and oxygen for this purpose. 



Kinds of Bodily Energy. The healthy body has at any 

 time a considerable amount of potential, or reserve, energy, 

 energy which it is not using at the time, but which it is 

 able to use as its needs require. When put to use, this 

 energy is converted into such forms of kinetic energy 1 as 

 are indicated by the different kinds of bodily power. These 

 are as follows : 



I. Power of Motion. The body can move itself from 

 place to place and it can give motion to things about it. 



1 Energy, which is defined as the ability to do work, or to cause motion, exists in 

 two general types, or forms, known as kinetic energy and as potential energy. 

 Kinetic energy is energy at work, or energy in the act of producing motion ; while 

 potential energy is reserve, or stored, energy. All moving bodies have kinetic 

 energy, and all stationary bodies which have within them the capability of causing 

 motion possess potential energy. A bent bow, a piece of stretched rubber, a sus- 

 pended weight, the water above a mill dam, all have the capability of causing 

 motion and all have potential energy. Examples of kinetic energy are found in 

 the movements of machinery, in steam and electricity, in winds, and in currents of 

 water. Kinetic is the active, and potential the inactive, form of energy. 



186 



