192 ELECTROCHEMISTRY 



because it involves the creation of a trivalent carbon atom and 

 the independent existence of an unsaturated radical. Free radi- 

 cals containing trivalent carbon have been prepared from com- 

 pounds belonging to a wide variety of types, and, more recently 

 the existence of divalent nitrogen has also been recognized. 

 With facts such as these in mind the customary stability of any 

 linkage in the simpler types of organic compounds no longer 

 suffices as a priori evidence of the impossibility of its rupture in 

 compounds of such a type as to expose it to strains of very un- 

 usual magnitude. Now the protein molecule weighing no less 

 than from 10,000 to 20,000 and consisting of a large number of 

 amino-acids linked together in long chains must evidently be 

 subject to exceptional strains. Just as a long thin bar of ma- 

 terial, no matter how great its strength, will, ultimately, if suffi- 

 ciently long and unsupported, break of its own weight, so in the 

 long chain of atoms composing a protein molecule, rupture of 

 linkages may occur which are sufficiently strong to resist all the 

 strains to which shorter or more symmetrical molecules are com- 

 monly subjected. It may of course be urged that this argument 

 proves too much, since, by parity of reasoning, the split of the 

 linkage between carbon and nitrogen should occur at all times and 

 not be dependent upon salt-formation, the additional strain im- 

 posed by the weight of a molecule of hydrochloric acid or sodium 

 hydroxide being negligible in comparison with the total strain to 

 which the molecule is subjected. It must be remembered, how- 

 ever, that the additional strains which a molecule of acid or base 

 introduces into the molecule are not merely those commensurate 

 with and attributable to its weight, but also strains of electrostatic 

 origin, since the salt which is formed unquestionably undergoes 

 ionization. It may very possibly be true that the first step in 

 salt formation consists in the neutralization of end — NHo or 

 — COOH groups, but that the ionization of the compound formed, 

 leading to the development of electrostatic tension at the very 

 places at which it must exert the greatest strain, namely the ex- 

 tremities of the molecule, results in the splitting of the otherwise 

 stable linkage — C = N— and the redistribution of the compo- 



I 

 nents of the molecule and the strains to which it is subjected. 



6. Biological Applications; the "Selective" Action of Living 

 Tissues. — The non-dissociable character of the inorganic con- 



