RATES OF LETHAL ACTION IX A CELL POPULATION 



591 



susceptibilities of the cells or organisms to the inhibitor. A curve obtained 

 by plotting the fraction of cells killed (or surviving) against the time of 

 exposure to the inhibitor cannot be interpreted directly as an expression 

 of inhibition rates. With respect to a single cell, one is dealing here with 

 an all-or-none phenomenon, namely the death of the cell, and the course 



'0 30 



TIME (MIN) 



IXIO 



25 50 



TIME (MIN) FOR 50% INHIBITION - 



75 



100 



Fig. 12-32. Inhibition of goat erythrocyte acetylchoHnesterase by 

 p-nitrophenyl diethylphosphate (E-600). The upper curves show 

 the effect of the inhibitor concentration on the rate of inhibition. 

 Curve A, 1.04 x 10-^ niJf; curve B, 1.95 X IQ-^ mM; curve C, 

 3.90 X 10-^ mM; curve D, 4.16 X 10-^ mM; curve E, 7.80 X lO-^ 

 m^M. The lower plot (Eq. 12-87) enables the bimolecular rate con- 

 stant to be determined {k = 1.1 X 10^ liters mole-^ min-^). 



of the effects within the cell leading to death is not measured. To illustrate 

 this let us take an extreme case. Assume that each cell in the poi^oulation 

 has the same susceptibility to the inhibitor. In the presence of a lethal 

 concentration of the inhibitor, all of the cells would die simultaneously 

 after a latent period determined by all the rates of the processes induced 



