CHAPTER II 

 CHEMICAL COMPOSITION OF THE BODY 



Everyone feels that he knows the difference between an 

 object that is alive and one that is not alive; and certainly 

 there is no difficulty in distinguishing between them when we 

 are considering such things as dogs and stones. But how can 

 we tell whether or not a dried pea is alive? We might find 

 out, perhaps, by planting it. If it sprouted, we should know 

 that it had life, but we could not tell by its appearance nor 

 by pulling it to pieces. 



When it proves impossible to tell the nature of a material 

 from surface examination or by dissection, the chemist is 

 usually called in to settle the question. It would be natural 

 to suppose that living and non-living bodies are made of 

 different chemical materials; that the living body contains 

 some hidden, secret thing which the non-living lacks. 



ELEMENTS 



For a century or more chemists have been at work trying 

 to divide things into the simple materials of which they 

 are made. Those simple materials which cannot be further 

 divided are called elements. Out of one or more of them, all 

 the various kinds of material in the world are made. Rather 

 to our surprise we find that there are but a small number 

 of elements, only about eighty-one being known of which 

 less than twenty make up most of the common things. 

 This seems a remarkably small number until we learn how 

 many different things can be made from the same ele- 



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