92 



TEE GROWTH AND DEATH OF BACTERIA 



The generation time during the logarithmic phase is influenced by several 

 factors. 



(1) Temperature of Incubation of Culture. — Working with Bad. coli, Chick 

 (1912) found that between 20° and 40° C, each rise of 1° C. increased the 

 rate of growth 1-072 times ; the temperature coefl&cient for every rise of 10° C. 

 was 1-072^'', i.e. 2-01. This agrees closely with Lane-Claypon's (1909) figure 

 of 2-2. Barber (1908), who made an exhaustive study of the rate of growth 

 of Bad. coli, constructed the curve shown in Fig. 17. In this it will be seen that 

 at a temperature of 15° C. the generation time is 180', at 25° C. 44', at 35° C. 22' 

 and at 40° C. 17'. The curve corresponds fairly closely to the quarter of an ellipse. 

 Further, as the increase is geometrical, by plotting the logarithms of the generation 

 times, we shall find that the points fall on a descending straight line. The maximum 

 rate of growth of Bad. coli occurs at about 37° C, but between 37° and 46° C. there 



_o 4 8 a 16 20 242832 364€4448 52 566064687276 eomsdsz demommmmmmmiszmMo 



Time, in Hours 



Fig. 18. 



A. Continuous line = Viable count of Salm. typhi-murium in peptone water. 



B. Interrupted line = Viable count of Salm. typhi-murium in peptone water + 2 per cent, glucose. 



(After Heap and Cadness.) 



is little change in the generation time. For Salm. typhi, Miiller (1895) found 

 the maximum rate of growth to be between 37° and 40-4° C. ; at a temperature of 

 44-5° C. the bacilli died rapidly. 



(2) Nature of Medium. — Penfold and Norris (1912) found that by increasing 

 the concentration of peptone in a peptone water medium from 0-125 per cent, 

 to 1 per cent., the generation time of Salm. typhi was reduced from almost infinity 

 to 40'. They likewise found that the addition of glucose to the medium further 

 reduced the generation time. Other workers have also commented on the beneficial 

 effect of glucose ; thus Heap and Cadness (1924) found that the addition of 2 per 

 cent, glucose to a 3 per cent, peptone water medium greatly increased the growth 

 of Salm. typhi-murium. (Fig. 18). 



(3) Nature of Organism. — Some organisms appear to grow more rapidly than 

 others. Mason (1935) has compiled from the literature the generation times of 



