324 



PHYSIOLOGY OF BACTERIA 



(1902) on the heat sterilization of spores of B. anthracis. In one 

 corner of the figure, the theoretical curves for different values of Qio 

 are shown. The angle with the abscissa determines the value of Q. 



Fig. 36. — Relation between temperature and thermal death times of 

 spores, illustrated by 15 thermophilic organisms, Clostridium botulinum, 

 and B. anthracis. The slope indicates the temperature coefficient, the 

 distance from the base the relative resistance to heat. 



If this curve were not plotted against logarithms of time, but 

 against time directly, the lines would not run straight, but in parallel 

 logarithmic curves. This type of curve is well known to the dairy 

 bacteriologist from the picture of Fig. 37 by North, which can be 

 found in many textbooks on milk pasteurization. The killing 

 times are exponential functions of the decreasing temperature. 

 Assuming Qio = 11 to hold for all bacteria, the time required to 

 kill a bacterium at 70°C. would be eleven times as long as at 

 80°C., and if the pasteurizing temperature is lowered another 10°C., 

 the killing time would have to be multiplied again by eleven. 



