4 OUR BODIES AND HOW WE LIVE 



7. The Body as a Self-Repairing Machine. The human 

 body and the locomotive are alike in another respect, 

 both are all the time wearing out. There is an important 

 difference, however, between the two. The locomotive 

 when badly worn must be taken to pieces and repaired by 

 the machinist. 



The human body, on the other hand, is constantly repair- 

 ing itself. We take food not only to warm us and to give 

 us muscular force, but also for the building up and repairing 

 of our bodies. 



Remember, then, that the body far surpasses the engine 

 in the perfection of its mechanism, inasmuch as it is a 

 self -repairing machine. 



CHEMICAL COMPOSITION OF THE BODY 



8. Chemical Elements in the Body. There are about 

 seventy different substances which, when pure, cannot be 

 broken into any simpler forms of matter. These are called 

 elements. 



The greater number of substances we see around us are 

 compounded of two or more elements. These compounds 

 may be broken up into simple elements by heat, and by 

 various other means. 



Our bodies are almost entirely composed of thirteen of 

 the seventy elements. Among these are oxygen, hydrogen, 

 nitrogen, carbon, and iron. 



Oxygen, hydrogen, and nitrogen, which are gases in 

 their uncombined form, make up three fourths of the weight 

 of the whole human body. 



Carbon, which exists in an impure state in charcoal, 

 forms more than one fifth of the weight of the body. 



