THE LAW OF EVOLUTION 



tion two molecules of oxygen, or four molecules 

 of hydrogen ; while three molecules of carbon 

 will hold four molecules of nitrogen. It follows 

 that in any organic compound, made up of the 

 four above-named elements, a large number of 

 molecules, possessing enormous mobility, must 

 be held in combination by a relatively small 

 number of molecules possessing little mobility. 

 And since it is a corollary from the persistence 

 of force that the sum of properties belong- 

 ing to any compound must be the resultant 

 of the properties belonging to its constituent 

 elements, it follows that a compound molecule 

 of organic matter must concentrate a great 

 amount of motion in a small space. If, for ex- 

 ample, we suppose ten molecules of carbon 

 united with four of oxygen, eight of hydrogen, 

 and eight of nitrogen, we shall have a com- 

 pound in which ten immobile molecules hold 

 together twenty highly mobile molecules. And 

 while the twenty retain much of their mobility, 

 the immobile ten prevent this mobility from 

 disintegrating the compound. 



Here we have reached a most beautiful and 

 marvellous truth. If we now proceed, secondly, 

 to follow out the way in which these quantitative 

 relations are compounded, the case will appear 

 still more remarkable. Instead of tens and 

 twenties, we have to deal with hundreds of inte- 

 grated molecules. Instead of such hypothetical 

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