CORRECTNESS OF THE CHEMICAL VIEWPOINT 63 



analyses by Dakin, 1 gelatin contains 1.4 per cent phenylalanme, 

 which would give as the minimal molecular weight of gelatin 

 11,800. Procter and Wilson's value leads to the result that 

 about 15, or a multiple of 15, molecules of a monobasic acid 

 combine with one molecule of gelatin. 



It can be stated, as the result of all these titration experiments, 

 that the ratios in which acids and bases combine with proteins 

 are identical with the ratios in which acids and bases combine 

 with crystalloids. Or, in other words, the forces by which 

 gelatin, egg albumin, and casein (and probably proteins in 

 general) combine with acids or alkalies are the purely chemical 

 forces of primary valency. 



The question may be raised, How can the fact that proteins 

 combine stoichiometrically be reconciled with the statement that 

 their solutions frequently contain aggregates of molecules? 

 This latter fact led to the assumption of adsorption at the surface 

 of each micella, but without cogent reason. The protein micellae 

 which may exist in a solution of gelatin in water are not compar- 

 able with metallic spheres or oil globules in water, where the two 

 phases are separated by a continuous boundary. When a 1 per 

 cent gelatin solution sets to a gel, the equal distribution of the 

 molecules of the gel in the water remains the same. The random 

 orientation of the gelatin molecules in the solution may change to 

 a more definite orientation in the gel, but the average distance 

 between the protein molecules will probably not change. The 

 interstices between the molecules remain the same, and the 

 protein molecules and protein ions remain as accessible to alkali 

 or acid in the gel as are molecules or ions in true solution. The 

 micellae of gelatin in solution are submicroscopic particles of jelly 

 and there is no reason why the reactions between gelatin and 

 electrolytes should not be stoichiometrical even if the protein 

 were entirely in the gel state. 



The titration experiments given in this chapter show also why 

 it is necessary to compare the relative efficiency of two kinds of 

 ions of the same sign not only for the same concentration of the 

 originally isoelectric protein but also for the same pH. As the 

 combination curves Figs. 6 and 8 show, at each pH only part of 

 the mass of the protein present exists in the form of a salt, the 



1 DAKIN, H. D., J. BioL Chem., vol. 44, p. 499, 1920. 



