NEW CONCEPTIONS IN SCIENCE 



uent is water. Barring bone, which is only a very 

 little alive, our bodies are more than three-fourths 

 water. Even bone is more than half, while our 

 brains are about nine-tenths water. Mixed with 

 water into a sort of gluelike solution, which may 

 become as hard as the enamel of the teeth, are the 

 various compounds of the four elements carbon, 

 oxygen, nitrogen, and hydrogen, which we daily 

 take in. 



This peculiar substance exhibits two especial 

 characteristics. Its assemblages of atoms, its mole- 

 cules, as chemists say, may grow, and by splitting 

 in two, reproduce ; that is what happens when the 

 grains of corn become a waving field; it is what 

 happens when the egg becomes a soaring eagle. 

 This is the first vital characteristic; the second is 

 that this living substance is irritable. 



This power of reacting to stimuli, which Claude 

 Bernard called irritability, is in some sort possessed 

 by all matter, but by living substance in a para- 

 mount degree. It is this characteristic which, 

 more than anything else, distinguishes the living 

 organism. Thinking substance is a kind of in- 

 tensified living substance. 



At first the line of demarcation is wholly absent. 

 The different parts of a coral polyp react equally 

 well to any outside influence. But very early in 

 the scale a difference begins to appear ; we find what 



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