JOHN H. NORTHROP 509 



hydrolysis of any two substrate concentrations is independent of the 

 quantity of enzyme used to make the comparison. 



2. The rate of hydrolysis is independent of the viscosity of the 

 solution. 



3. The percentage retardation of the rate of hydrolysis by inhibit- 

 ing substances, is independent of the substrate concentration. 



4. There is experimental evidence that the enzyme and inhibiting 

 substance are combined to form a widely dissociated compound. 



5. If the substrate were also combined with the enzyme, an increase 

 in the substrate concentration should affect the equilibrium between 

 the enzyme and the inhibiting substance. This is not the case. 



6. The rate of digestion of a mixture of casein and gelatin is equal 

 to the sum of the rates of hydrolysis of the two substances alone, as 

 it should be if the rate is proportional to the concentration of free 

 enzyme. This contradicts the saturation hypothesis. 



7. If the reaction is followed by determining directly the change 

 in the substrate concentration, it is found that this change agrees 

 with the law of mass action; i.e., the rate of digestion is proportional 

 to the substrate concentration. 



Most of the experimental work in this paper was done by Mr. 

 Frank Johnston. 



