December 29, 1922] 



SCIENCE 



739 



stating that the so-«all6d colloidal behavior of 

 protein solutions, as far as osmotic pressure is 

 concerned, is merely the result of an equilib- 

 rium eondition of dassical chemistry -which re- 

 sults in an excess of the concentration of 

 crystalloidal ions inside the protein solution 

 over ithat of an outside aqueous solution, when 

 the two solutions are separated by a membrane 

 AvMch is permeable to crystalloidal ions but 

 impermeable to protein ions. The colloidal 

 behavior of proteins depends therefore entirely 

 on the relative non-diffusibility of protein ions 

 through membranes which are easily permeaible 

 to crystalloidal ions. Since the majority of 

 membranes in plants and animals belong to tMs 

 dass, it can easily ibe surmised how great a 

 role the proteins must play in the regulation of 

 osmofcie pressure in the body. 



VI 



It remains to show briefly why swelling and 

 viscosity of protein solutions are affected in a 

 similar way by electrolytes as is the osmotic 

 pressure. The answer is that we are dealing 

 in both cases with the same fundamental prop- 

 erty, namely, osmotic pi-essure. 



In 1910 Procter made the ingenious sugges- 

 'tion that the swelling of gelatin mig-ht be an 

 osmotic phenomenon and in subsequent papers 

 he and J. A. Wilson put this theory on a quan- 

 titative basis by deriving it from the Donnan 

 equilibrium. They showed that the swelling of 

 a solid gel of gelatin in hydrochloric acid can 

 be explained quantitatively on the (basis of the 

 Donnan equilibrium on the assumption that 

 there exists an excess of concentration of 

 crystalloidal ions inside (in this case H and CI) 

 over the concentration of the same ions outside, 

 and that the excess of osmotic pressure inside 

 . the gel over that outside due to this Donnan 

 effect accounts for that share of the swelling 

 which is caused by the influence of the acid. The 

 agreement of their calculated values with the 

 obsei-ved values ■ is excellent. The writer is 

 inclined to consider Procter's theory of swell- 

 ing and the proof of this theory by Procter 

 and J. A. Wilson as the most brilliant con- 

 tribution to the theory of colloidal behavior 

 next in importance only to Donnan's theoiy of 



membrane equilibria. There was only one de- 

 tail left by these authors, namely, to prove the 

 existence of membrane potentialls between the 

 gel and the surrounding aqueous solution at 

 equililbrium. The writer was able to fill this 

 gap and to show that the observed P.D. totween 

 gel and surrounding aqueous solution can be 

 CE^lculated wdth a fair degree of accuracy from 

 the value Pn inside minus Pn outside with the 

 aid of Nernst's logarithmic formula. 



VII 



It may seem strange that the influence of 

 electrolytes on the viscosity of certain protein 

 solutions should be explained in the same way, 

 but this seems to be the case. According to 

 Einstein's formula, the viscosity of an aqueous 

 protein solution is a linear function of the 

 relative vCliune of the solute occupied in the 

 solution, as expressed in the formula 



71 = 7|„(1 + 2.5?) 



where 7) is the viscosity of the solution, -rig that 

 of pure water, and 9 the proportion of the 

 volume of 'the solute to that of the solution. 

 If, therefore, the addition of little acid to a 

 1 per cent, solution of isoelectric gelatin 

 increases the viscosity of tbe so^lution until a 

 maximum is reached and if the addition of 

 more acid depresses the viscosity again, it fol- 

 lows that the addition of acid changes the rela- 

 tive volume occupied by the gelatin in water. 

 This is only possible by water being absorbed 

 by the protein and the question is how to ac- 

 count for this absorption of water by the pro- 

 tein under the influence of acid. Pauli assumed 

 that the ionized protein surrounds itself with a 

 jacket of water which is lacking in the non- 

 ionized protein. If this were true, all the pro- 

 teins and amino-acids should show such an 

 influence of acid on the viscosity of their solu- 

 tions. The writer found that no such influence 

 exists in the case of amino-aoids and at least 

 one protein, namely, crystalline egg albumin; 

 if Pauli's assumption were correct, there is no 

 reason why crystalline egg albumin should not 

 show the same influence of acid on viscosity 

 which is found in the case of gelatin. The dif- 

 ference between gelatin and crystalline egg 

 albumin is that the former sets to a solid gel 



