CHAPTER TWO 



THE LIVING SUBSTANCE 



1. LIFE, as we know it, is manifested only by pro- Protoplasm 

 toplasm. This protoplasm, or primal material of life, 



is a translucent, jelly-like substance, seeming on in- 

 spection to have no definite structure. The amount 

 occurring in a single mass is, however, quite limited ; 

 the protoplasm of the living body is broken up into 

 innumerable separate though contiguous units, called 

 the cells. 



While we speak of the living material as protoplasm, 

 the word must be understood to indicate not a single 

 sort of substance, but a whole class of substances 

 differing in minute though very significant details. 

 The protoplasm of man is not the protoplasm of the 

 worm or flower ; yet it is convenient to have a single 

 word to designate all living material, which, however 

 diverse in details, is fundamentally similar in all cases. 

 This essential similarity has been strongly emphasized 

 by recent experimental work, which shows that it is 

 possible, up to a certain point, to reason from the 

 life phenomena of plants to those of animals, or vice 

 versa. 



2. What, then, is this protoplasm ? It is a mixture chemistry 

 of complex chemical compounds, consisting of car- 



bon, oxygen, hydrogen, nitrogen, and other elements. 

 Such a statement conveys little to the mind, especially 

 if we recall these elements in their pure form - - car- 

 bon as charcoal or diamond, the other three as invisible 

 gases. A chemical analysis may give us all these 

 elementary bodies, in certain proportions, but we are 

 scarcely more edified than we should be if shown the 

 paints out of which a splendid picture had been made. 



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