SPECIFIC AND NONSPECIFIC RESISTANCE 



as the time required for the numbers of bacteria present to double 

 in population. 



Constant temperature water baths which maintained the specified 

 temperature ± 0.5° C were employed in all the experiments. 



Effect of varying temperatures on oxygen uptake . Figures 1 and 2 

 show that a number of different curves are obtained when oxygen 

 uptake is plotted as a function of time for a given temperature. The 

 results appear identical with the strains employed in K. pneumoniae 

 and S. aureus. A significant decrease in oxygen uptake occurs at 

 32° C compared to that occurring at 37° C. At temperatures below 

 32° C, the oxygen uptake rates are again lessened, but little change 

 is noted between 20° C and 25° C. It is of interest that the S. aureus 

 oxygen uptake is significantly lower than that of K. pneumoniae 

 when the same temperatures are compared. 



Effect of varying temperatures on growth and generation 

 times. Calibrated cuvettes (13 x 100 mm) containing 5 ml of tryptose 

 phosphate broth were seeded with a standard loop (0,01 ml) of 

 broth inoculum obtained from an 18-hour culture. The optical 

 density was measured at zero time and thereafter at various 

 increments of time. Duplicate sets of cuvettes were employed. 

 The number of organisms for any given period of time was de- 

 termined by reference to a standard curve. The results are 

 shown in Figures 3 and 4, 



It is seen that similar results were obtained with the strains 

 of K, pneumoniae and ^ aureus. In both cases, families of curves 

 were obtained. The slopes of the curves are not significantly 

 different from each other, incj^icating that the generation time at 

 temperatures ranging from 37° C to 25° C are not markedly 

 affected by different temperatures, but a noticeable increase in 

 the lag phase is seen. No measurable increase in turbidity occurred 

 at temperatures below 25° C, It is possible that, for the time 

 employed, multiplication did not occur or was too slow to be 

 measured by this technique. 



161 



