CHAPTER I 



LIVING MATTER 



Organisms Composed of Living Substance. — Every 

 organism is composed mainly of living substance. Its 

 characteristics, functions and powers are dependent on 

 the nature of the living substance. If then we are to un- 

 derstand the physiology of any plant or any animal we 

 must know something about this substance. We must 

 study it, not in its most highly developed form, as it ap- 

 pears, for instance, in the muscles and nerves of human 

 beings, but in its simplest state. We shall then find out 

 what the characteristics are that distinguish it from 

 everything else. These characteristics are few and 

 always the same. They may become more complex 

 as the result of some special development, but no 

 matter how highly developed this substance may be, 

 it can not take on new powers, it can only develop and 

 modify those that belong to it simply because it is alive. 



Appearance of Living Substance. — If we scrape a few 

 hairs from the stamen of such a flower as the wandering 

 jew and examine them with a compound microscope we 

 can see what this substance looks like. Each hair is 

 made up of a series of compartments which appear more 

 or less transparent (Fig. 1, A). Within the trans- 

 parent space in each compartment a shadowy, granular 



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