JACQUES LOEB 41 



show in this paper that gelatin on the alkah or less acid side of its 

 isoelectric point can combine only with the cations of neutral salts, 

 as we had actually found empirically in our previously published 

 papers. 



Moreover, it will follow from the experiments to be published in 

 this paper that the gelatin ion can dissociate electrolytically only 

 as one of the two, either as a cation or as an anion but not as both 

 simultaneously (except to a negligible degree) , and that the hydrogen 

 ion concentration of the solution alone determines in which of the two 

 ways it dissociates. We shall also show that the isoelectric point is 

 not only the point where the gelatin sends out as many H as OH ions 

 but that it is the point where it apparently sends out neither; i.e., 

 where it cannot exist in an ionized condition at all. 



II. 



Our method of testing whether gelatin reacts with the cation or the 

 anion of a neutral salt is based on the difference of the effects of uni- 

 valent and bivalent ions upon gelatin. It was found in the writer's 

 experiments on osmotic pressure, viscosity, alcohol precipitation, and 

 swelling that a salt of the type Na2S04 (univalent cation, bivalent 

 anion) of a certain molecular concentration, e.g. m/128, has quantita- 

 tively and qualitatively the same effect upon gelatin (pH = 7.0) as a 

 salt of the type NaCl at the molecular concentration m:/64; i.e., twice 

 the molecular concentration of the Na2S04.^ This proves that only 

 the cation of the salt and not the anion acts upon the gelatin. It 

 was found, moreover, that all neutral salts with monovalent cation 

 (Li, Na, K, NH4) cause an increase in osmotic pressure, viscosity, 

 alcohol number, and swelling of gelatin, while salts with a bivalent 

 cation (Mg, Ca, Sr, Ba, Co, Mn) cause no such increase; and if a 

 salt with bivalent cation is added in small quantity to a large quan- 

 tity of a salt with univalent cation, the increase in osmotic pressure, 

 viscosity, alcohol number, and swelling caused by the salt with uni- 

 valent cation is inhibited (antagonistic salt action).' The sama is 



^ Loeb, /. Biol. Chem., 1918, xxxiv, 77, 489. 



