745 



mine the action of pepsin. Here tlie pepsin solution acts on carmin- 

 stained fibrin. Tlie stain of the fluid varies with the quantity of fibrin 

 dissolved; the intensity of the stain, being an index: of the peptic 

 action, is determined colorimetrically. 



According to Michaelis' observations the action of pepsin depends 

 entirely on the H-ion -concentration, that is to say various acid, 

 render the pepsin equally active, provided only (hat this concen- 

 tration is the same for every one of them. In trying to ascertain 

 this after Ghütznkr's method, I arrived at different results. It appeared 

 first and foremost that the action of every acid corresponded to the 

 swelling of the fibrin. The o[)limum of the digestion lay at that 

 reaction whicii concurred with a maximum swelling. I found this 

 to be the case for hydrochloric acid, oxalic acid, lactic acid, phos- 

 phoric acid, sulfuric acid and citric acid. It is peculiar that in 

 acetic acid the swelling occurs nol only in highly aqueous solutions, 

 but also in sparingly aqueous solutions, from which I inferred that 

 in the latter the swelling is brought about by the combination with 

 the acetic acid and not with water. Acetic acid and water are 

 similar in their behaviour also in other respects. Be this as it may, 

 the action of the pepsin corresponded to the swelling in solutions 

 containing much water, not in the sparingly aqueous solutions ; 

 probably the enzyme acts only on protein swollen up by water, 

 not by acetic acid. 



When comparing the action in the various acid solutions at their 

 optimal H-ion-concentralion, this action appeared to differ rather 

 much. On the ground of Michaelis' views the optima as well as the 

 activity might be expected to be all alike for all acids. The con- 

 dition of the pepsin, as determined by the Cii, should, according to 

 Michaelis, be most fa\ourable at a definite Cn, no matter by what 

 acid the Cn is evolved. As stated before, my results go against this 

 theory, as is shown by the table on p. 74(i. 



The values of pu and Cn before the action of the pepsin illustrate 

 best the optimal reactions ; after the digestion these values under- 

 went various changes in proportion to the progress of the digestion. 

 With sulfuric acid the reaction has even become alkaline, which is 

 owing to the peculiar action of sulfuric acid. I did not notice it 

 with any of the other acids, whatever the concentration may have 

 been. It seems that sulfuric acid has liberated the ammonia, with 

 which the carmin was still urtited, and that it was in its turn 

 combined with or adsorbed by the fibrin or the carmin. We see 

 now how much the optima (before the action of the jjepsin) differ; 

 with phosphoric acid the Cn is highest, 0.011 ; and with acetic acid 



48* 



