32 JOHN H. NORTHROP 



of such autocatalytic curves calculated by the autocatalytic equation for 

 the conditions that i, 5, 10, or 20 per cent of the final maximum number 

 of molecules are present at the beginning. The curves show that after 

 the first part of the reaction the increase in the number of molecules 

 formed after a given time interval increases much more slowly than does 

 the original number. For instance (Table I), after 2.0 minutes, 50 



TABLE I 



Value of A corresponding to different values of Ao after different time 



intervals 



2.3 A{A—Ao) 



Calculated from Autocatalytic Equation, T = Log 



KAe Ao(Ae-A) 



K — .023 ; Ae= 100 -{- Ao; At =^ Number of particles present at time 



T (mins.) 



molecules would be present if one were present at the beginning, whereas 

 only 115 would be present if twenty were present at the beginning. 

 After 3.0 minutes the corresponding figures are 90 and 118. These 

 figures are similar to those actually found by Delbriick and Luria. They 

 were calculated on the assumption that the reaction followed the theo- 

 retical course. Actually the effect of changing the total concentration 

 on the rate of enzyme reactions is usually less than that predicted by 

 simple theory. This effect would tend to decrease the difference in the 

 figures given above. 



3. If the number of molecules liberated per bacterial cell is actually 

 constant and independent of the infective quantity as Delbriick and 

 Luria suggest, then it is necessary to assume that the liberation occurs 

 as soon as the virus-forming reaction is completed. This assumption 

 predicts also that lysis occurs as soon as the ratio of virus to bacteria 

 reaches a definite value. This result agrees with the experiments of 

 Krueger and Northrop (1930). If liberation of virus occurs as soon as 

 this constant amount of virus is formed, the time required should be 

 shorter as the number of infective units increases, although the varia- 



