749 



fact we may conclude, tliat the action caused bj the acid alone may 

 be the same as that, brought about by pepsin in acid solution, though 

 it is slower. Both actions consist in splitting the large protein 

 molecules; the problem is really very complex; the splitting yields 

 new products with other properties, and consequently another 

 situation of the maximum of the swelling. The initial viscosity 

 determined directly after the addition of the acid, can only, if ray 

 judgment be connect, be an index of the action, which the pepsin 

 can exert on the protein molecules present at the beginning. Most 

 likely' the new products, gradually evolved, reach the maximum 

 swelling at another degree of acidity than the original protein. 

 Unfortunately these products of decomposition seem to have little 

 intluence on the viscosity also in their swollen state, so that we 

 cannot observe the swelling with regard to these products with 

 great accuracy. From this it follows that we can hardly speak of 

 the maximum of swelling of dissolved protein with a definite amount 

 of acid at which pepsin acts best, but that in reality this maximum 

 must necessarily shift according to the formation of other substances, 

 even though the shifting cannot be extensive, because first of all, 

 the decomposition products are, as far as their properties are concerned, 

 very similar to the original protein, and secondly because with 

 pepsin the decomposition does not advance far. In addition there is 

 the practical difficulty that during the digestion the reaction must 

 necessarily change. We are also aware that pepsin, especially in 

 solutions with a very small amount of acid and also in such as 

 have a large amount of it, gradually loses its activity. Finally, even 

 from the modification of the viscosity in the strong acid solutions, 

 without pepsin, it appears that the action of acid alone must not 

 be ignored. 



When recapitulating we can slate that: 



1. Under the influence of the acid the maximum of the viscosity, 

 as iletermined by us, has shifted a little towards the small amounts 

 of acid. 



2. The location of the maxima of the swelling cannot be expected 

 to be entirely constant, when the protein is split up; as yet we 

 cannot say in what direction the shifting takes place. 



3. The activity- of pepsin gradually slackens, especially in the 

 weak acid solutions, however also in very strong acid solutions. In 

 consequence of this, it is especially in prolonged experiments that 

 the optimum of the activity of pepsin shifts towards the stronger 

 acid solutions. 



4. Also the acid itself occasions a certain digestion, which shows 



