EQUILIBRIA IN ABSORPTION PROCESSES 161 



but to confine our studies to the albuminous substances 

 if we wish to understand the processes going on in living 

 matter. 1 



One of the properties of albuminous substances which 

 was regarded as proving their colloidal nature was pre- 

 cisely the migration of these substances in the electric 

 field. Dialysed serum, says Pauli, does not migrate, but 

 if we add an acid, the egg-white follows the positive cur- 

 rent ; if we add an alkali to the solution, it travels to the 

 positive side. This circumstance is explained by the 

 adherents of the colloidal theory by the assumption that 

 the egg-white absorbs positive H ions or negative OH ions. 

 As Bredig, Freundlich, and Loeb 2 have remarked, this 

 follows at once from the well-known fact that proteins are 

 amphoteric electrolytes, which form salts as well with 

 acids as with bases, just as do the amido-acids, e,g. glyco- 

 coll, with which substances the albumins are even very 

 closely related according to the recent investigations of 

 Kossel and E. Fischer. It is quite true that, just as 

 ammonia by adding an hydrogen ion forms the ammonium 

 ion, in quite the same manner the amido-group of the 

 albuminous substance adds hydrogen and gives an albumin 

 ion. But there is a very great difference between an ion 

 and the suspended particles (e.g. of kaolin) which obtain 

 a positive change through the influence of dielectric forces. 

 That the albuminous substance really so behaves, that it 

 adds a hydrogen ion and gives an albumin ion, i.e. that 

 the addition of an acid to it gives rise to a real neutralisa- 



1 Pauli : Naturiu. Rundschau, p. 3 (1906). 



2 Cf. Loeb : Vorlesungen iiber die Dynamik der Lebenscrschcinungen, 

 pp. 65-67, Leipzig (1906). 



