354 THE HUMAN MACHINE 



units or cells unless we use a microscope. Food helps 

 to build these cells, and in a growing boy or girl the 

 number of cells is constantly increasing. Food also gives 

 off energy when it is oxidized or burned in the body. 

 Each kind of cell, muscle, bone, or nerve has its work 

 to do. This work means expenditure of energy the 

 energy we get from our food which is distributed to the 

 cells by means of the blood. There in the cells, and 

 there only, the food is actually oxidized, and gives off 

 energy in the form of heat, to do our work. 



But you ask, how can pieces of solid food get into these 

 tiny cells ? Food is of no value to the body until it does 

 get into the cells, and to do this it must be in the form 

 of a liquid. This is done by a process we call digestion, 

 during which food changed from a solid to a liquid form. 

 In this condition it may be absorbed or taken up by the 

 blood, then circulated to various parts of the body. 

 Finally, it enters the cells or individual units of the body, 

 where it is actually used. The pages which follow will 

 help us understand a little more about the care of this 

 most wonderful of all machines, the human body. 



PROBLEM I. HOW DOES THE HUMAN MACHINE 

 DIFFER FROM AN AUTOMOBILE? 



How an Automobile and the Human Machine Are Alike. 



At first sight the human body does not seem much like an 

 automobile and yet we can see many ways in which they 

 are alike. Both have a framework which holds them 

 up in the auto it is metal, in the body, the bony 

 skeleton. Both have protective coverings, the glossy 

 paint finish in the auto, the skin in the body. Both 

 consume fuel and use it in the same way to release energy 

 or power to do work. The gears and wheels transmit 

 the power in the automobile, while in the human machine 



