R. E. BUCHANAN 57 



The size and constancy of the thermal increment ^ may be determined either by 

 substitution of values in equation (24) or by plotting the logarithm (base e) of k against 

 the reciprocal of the absolute temperature. Such a graph is given in Figure 7 for 

 the effect of temperature upon the growth of a bacterial culture between 0° and 30° C. 

 It will be noted that the points apparently determine in this case two intersecting 

 straight lines. Crozier and others interpret a finding of this type as indicating a 

 change at a certain temperature from one basic reaction in the catenary series to an- 

 other as governing the growth rates. Graphs of this type are made most conveniently 

 by using a semilog paper in which the abscissae are indicated as temperatures centi- 

 grade but are spaced in proportion to the value of the corresponding reciprocal of the 

 absolute temperature. The data of Figure 7 are plotted on this type of co-ordinate 

 paper in Figure 8. 



It is evident that if values of the thermal increment are known, and the relation- 

 ships outlined above hold, it is possible to predict the form which growth curves will 

 assume at different temperatures. 



