282 PHYSIOLOGY OF BACTERIA 



log a is constant within the experiment. Therefore, we 

 have 



log 6 = C - 0.434Z^ 



which means that the number of survivors is a logarithmic 

 function of the time. For this reason, this regularity of 

 death is often referred to as the ^logarithmic order of 

 death." If we consider log 6 to be a variable, instead 

 h itself, we get the general formula of a straight line 



y = C - 0Ad4:Kt 



This means that if we plot the logarithms of survivors 

 against time, all points will be on a straight line. Figure 

 31 shows the survivors of spores of B. anthracis exposed to 

 three different temperatures plotted in this way, from 

 an experiment by Eijkman (1912-13). The logarithmic 

 survivor curves are straight lines, the different angles 

 indicating different death rates. 



In recent years, several investigators have been satisfied that 

 the logarithmic order is proved whenever the logarithms of survivors 

 are found to be on a straight line. 



The most essential point in this kind of graphic proof is the inclu- 

 sion of the initial number of cells in the curve. If this is not included 

 in the graph, a straight line relationship proves nothing. As may 

 be seen from Fig. 32, most of the curves indicating quite different 

 orders of death are so nearly a straight line that they would be 

 considered so from experimental data, if the first horizontal part 

 of the curve were omitted. It is very essential to ascertain whether 

 or not there is an initial period without deaths. The omission of 

 the initial number makes this impossible. Only a constant death 

 rate can then be considered proof of a logarithmic order of death. 



(d) INTERPRETATIONS OF THE ORDER OF DEATH 



This order of death is, in its mathematical aspects, a 

 complete parallel to the monomolecular reactions. What 

 the chemist calls ''rate of reaction" or ''reaction veloc- 



