746 



TABLE III. The action of pepsin in different acid solutions at the optimal reactions. 

 Time: 5 minutes. 



it is lowest, viz 0.003. It is also obvious how unlike the digestion 

 is witli the various acids; also, however, that the swelling corresponds 

 fairly to this digestion, except with acetic acid, the beiiaviour of 

 wliich substance has ah-eady been discussed. What strikes us most 

 is the very low digestion in tiie sulfuric acid solution and the con- 

 currence of a minimal swelling. I, therefore, disagree with Mich.aei.is 

 and his pupils with regard to their assertion that it is virtually 

 only the Cn wiiich determines the action of the pepsin. Pepsin 

 works best in those solutions in which the proteins swell most. This 

 maximum by no means occurs at the same H-ion-concentration with 

 di.Terent acids; when the anion is highly hydrophilous, as is the 

 case with sulfuric acid, the action of this ion prevails even in com- 

 paratively slight concentration, the optimum of digestion then lies 

 at low Cu, and the digestion is inappreciable, since the swelling 

 can be but slight. 



The relation between digestion and swelling becomes even more 

 manifest, when we study the influence of salts. Salts were known 

 to generally impede the action of pepsin. Even common salt does 

 so very strongly in a concentration as in seawater; the action of 

 sulfates especially is verj- inhibilory. Up to now nothing was known 

 about the cause of this action of salts. Michaelis speaks of a "Salz- 

 wirkung" noticeable also in the shifting of the optima to the smaller 

 di. When looked upon from my standpoint, the action of the salts 

 is quite easy to explain and we are even enabled to say before- 

 hand which salts arrest the action considerably and which are only 

 slightly inhibitory, since salts markedly affect the swelling of protein 



