The Making of Species 



extend this list. It must suffice that almost 

 every investigator of the phenomena of inherit- 

 ance believes in these units, and calls them 

 by a different name. Moreover, each clothes 

 them with characteristics according to his taste 

 or the fertility of his imagination. 



These units behave in such a way as to sug- 

 gest to us an analogy between them and the 

 chemical molecules. The sexual act would appear 

 to resemble a chemical synthesis in some respects. 

 One of the most remarkable phenomena of 

 chemistry is that of isomerism. It not in- 

 frequently happens that two very dissimilar 

 substances are found, upon analysis, to have the 

 same chemical composition, that is to say, their 

 molecules are found to be composed of the same 

 kind of atoms and the same number of these. 

 Thus chemists are compelled to believe that the 

 properties of a molecule are dependent, not only 

 on the nature of the atoms which compose it, but 

 also on the arrangement of these within the 

 molecule. To take a concrete example : Analysis 

 shows that both alcohol and ether are represented 

 by the chemical formula C 2 H 6 O. In other words, 

 the molecule of each of these compounds is made 

 up of two atoms of the element Carbon, six of 

 the element Hydrogen, and one of the element 

 Oxygen. Now, every chemical atom possesses the 

 property which chemists term valency, in other 

 words, the number of other atoms with which 



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