28 A. KOHN AND M. LION 



very much the curve of inactivation of the virus of poHomy- 

 ehtis by formalin"^''. In both cases the lethal agent (oxygen or 

 formalin) is in excess and its concentration does not change 

 during the process of inactivation; in both cases the relative 

 mortality of the viruses or bacteria is independent of their 

 initial concentration. 



Card's empirical formula that may be fitted to the curve of 

 inactivation is 



In — := a\n{\ + bt) (1) 



where yo is the viability of the virus at time 0, y the viability at 

 time / and a and b are constants. For infinite time of reaction, a 

 plot of log viability of cells against log time gives a straight line. 

 If F is the concentration of formalin and C a constant, the 

 kinetic equation derivable from the above would be of the form 



—dy 



= K.F.v 



dt 



Ko 



where K = — — and is a function of time. In the case of 



1 + Crt 



poliomyelitis, the change of the inactivation constant is ex- 

 plained by a change in resistance of the virus to the action of 

 formaldehyde in the course of the treatment, presumably 

 because of change in the permeability of the virus membrane. 

 As regards oxygen, one may postulate the existence in the 

 bacterial cell of several sensitive targets (the metastable meta- 

 bolic intermediates) that have different inactivation constants 

 with regard to oxygen, the reaction of oxygen with a single 

 molecule being of first order. The velocity of reaction between 

 the cell and the oxygen would be proportional to the number of 

 targets that have not yet reacted. The reaction constant, although 

 fundamentally of first order, becomes dependent on time, as 

 more and more targets (part of them vital) are knocked out. 



