592 



12. RATES OF INHIBITION 



by the inhibitor and progressing to death. However, since it appears that 

 all cell populations show some type of variation between the individual 

 cells, the rate at which the cells die will be determined solely by this va- 

 riation. The absolute latent period 1)efore any cell deaths occur will be the 

 only measure of the rate at which tlie inhibitor penetrates into the cells 

 and exerts its final effect. 



The problem of the relationslii]) lietween the nature of the variation in 

 susceptibility and the time course of the lethal action will now be consid- 

 ered. If the distribution of susceptibility is symmetrical around the mean 

 susceptibility (Fig. 12-33, curve A), a characteristically symmetrical sig- 



5 



TIME (MIN) 



Fig. 12-33. Different distributions of susceptibility in cell popu- 

 lations. Curve A represents a symmetrical distribution (Eq. 12-88) 

 with a = 1 and 6 = 0.1. Curves B and C show hypothetical 

 skewed distributions. 



moid curve for the death rate is obtained (Fig. 12-34, curve A). It is as- 

 sumed here that the mean susceptibility is such that the greatest number 

 of cells die at 20 min after exposure to the inliibitor. and the curve is 

 plotted according to the equation: 



n = ae-"'' (12-88) 



where » = number of cells dying at any time t, and a and 6 are constants 

 that determine the form of the distrilnition curve. This form of equation 

 is usually accepted as representing most natural or luological distributions. 

 For the sake of simplicity, it has been assumed that there is no absolute la- 

 tent period, i.e., that the most susceptible cells begin to die immediately. 

 If the variation is not symmetrical Init is skewed as in curve B of Fig. 12-32, 

 the death rate curve will be altered (Fig. 12-34, curve B). If the distribution 

 is very asymmetrical as in curve C of Fig. 12-33, where the greatest number 

 of cells die immediatelv luit more resistant cells also occur, the death 



