222 HYDROGEN ION CONCENTRATION AND PEPSIN DIGESTION 



It can only be said that such a correction is necessary and that it 

 would be in the right sense. The divergence on the alkaline side is 

 probably due to the fact that the amount of hydrolysis selected as 

 the end-point represented too great a percentage change in the original 

 substrate concentration to assume that the substrate concentration 

 remained constant during the course of the experiment. 



TABLE II. 



pH, Conductivity, and Rate of Digestion of Gelatin Solutions. 

 Gelatin, 5 per cent dry weight in solution of total (approximate) concentra- 



EXPERIMENTAL. 



50 gm. (dry weight) of purified isoelectric gelatin were dissolved in warm water 

 and the volume was made up to 500 cc. Increasing amounts of HCl were then 

 added to a series of 50 cc. portions of this solution and the volume of each portion 

 was then made up to 100 cc. 2 cc. of 2 per cent pepsin solution were then 

 added to 75 cc. of each of the above solutions and the solutions put in the water 

 bath at 37°C. At short intervals 5 cc. samples were pipetted from each of the 

 solutions into a series of test-tubes containing 2 cc. of water. These tubes were 

 then placed in a water bath at 2°C. for 10 minutes, taken out, and the degree of 

 liquefaction was compared with that of a standard tube. (This is a slight modifi- 

 cation of the method of Fermi as described by Dernby.^^) This procedure was 

 repeated until a sample from each of the tubes showed the same degree of lique- 

 faction as the standard tube. In this way the time necessary to produce a certain 

 degree of liquefaction can be accurately and easily determined. The pH and con- 



27Dernby, K. G., /. Biol. Chem., 1918, xxxv, 179. 



