JOHN H. NORTHROP 



607 



the rate of digestion is plotted against the conductivity of the protein. 

 This figure shows that the two values are approximately directly 

 proportional. 



10 



«3 





2 4 8 12 16 20 24 28 32 



Specific conductivitij of solution due to protein salt x 10* 



Fig. 2. Rate of digestion and conductivity of egg albumin solutions. 



Viscosity of the Solution. 



It is impossible to use egg albumin in more concentrated solutions 

 than 16 per cent as the higher concentrations set to a jelly very rapidly. 

 It seemed quite possible that the increasing viscosity of the solution 

 might affect the rate of digestion (as found by Colin and Chaudim-'* 

 for invertase). This question can be tested experimentally by taking 

 advantage of the well known hysteresis of albumin solutions. 



500 cc. of a 25 per cent egg albumin solution were titrated to pH 1.6 with HCl, 

 placed at 25°, and the viscosity and rate of digestion of a sample determined at 

 intervals for about 10 hours. The amount of pepsin used was such that the vis- 

 cosity of the digesting solution did not change appreciably during the determina- 

 tion. This was due to the fact that the decrease in viscosity by the pepsin was 

 equallized by the increase of the viscosity with time. The viscosity of the solu- 

 tion at the beginning of the experiment was about three times that of water and 

 at the end too large to measure by the viscosimeter. At the beginning of the last 



^* Colin, H., and Chaudun, A., Compf. rend. Acad., 1919, clxix, 849. 



