218 THE FITNESS OF THE ENVIRONMENT 



trichloracetic acid, depend upon the number 

 of such foreign groups and their arrangement, 1 

 it is evident that the hydrocarbon radicals 

 have a constancy of influence upon the prop- 

 erties of the molecule which is not shared by 

 other radicals. 



The indifference of effect of hydrogen and 

 carbon, when linked to carbon, upon the 

 properties of the molecule is undoubtedly a 

 principal cause of the stability of complex 

 organic substances. Through this peculiar- 

 ity of the two elements the integrity of the 

 valence energy of carbon is preserved, and the 

 long carbon chains are stable. Whenever 

 the molecule becomes overloaded with radi- 

 cals of other kinds the strength of the tie 

 between carbon atoms diminishes and the 

 compound becomes unstable. The proper- 

 ties of the carbohydrates, which will be later 

 discussed, admirably illustrate such instabil- 

 ity. In short, organic compounds are in some 

 respects properly to be regarded as compounds 

 of carbon and hydrogen jointly, for it is not 

 the properties of carbon alone, but those of 

 carbon and hydrogen together which chiefly 

 \ make them possible. 



1 Henderson, Journal of Physical Chemistry, IX, 40, 1905 ; 

 Proceedings of the American Academy of Arts and Sciences, 

 XLII, 639, 1907; Zeitschrift fiir Physikalische Chemie, LX, 

 413, 1907. 



