LOGARITHMIC PHASE 



91 



The results are plotted on a graph whose abscissae represent T and whose ordinates 

 indicate the rate of propagation. The numerator and the first term of the denominator 

 in the formula represent the arithmetic increase in the number of organisms in unit time. 

 The second term or " suffix " of the denominator is not part of the divisor but indicates 

 the mid-point of the period during which the actual increase has occurred. The use of 

 the formula is exemplified in Table 3 and Fig. 16. 



It wUl be observed that, while the curve of the logarithms indicates that a steady 

 rate of multiplication is occurring during the 1-5 hour period, the curve given by Lemon's 



ZOO 

 190 

 180 

 170 

 160 

 150 

 140 



130 



(o 



^120 

 :s 



^ WO 



90 

 80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



1Z-5 15-0 17-5 ZO-0 22-5 250 275 300 325 35-0 37-5 40-0 42-5450 47-5 

 Decrees Centigrade 



Fig. 17. — The Growth Rate of Bad. coli at different Temperatures. 



Continuous Una = Curve plotted from actual observations. 

 Interrupted line = Smoothed curve. 

 (After Barber.) 



formula shows that the actual rate of arithmetic increase rises rapidly to reach a peak 

 at 5 hours, after which it falls steeply. The reason for the rapid rise is, not that the 

 organisms are dividing more rapidly at the end than at the beginning of the logarithmic 

 phase, but that, owing to the fact that the actual numbers of bacteria are constantly 

 increasing throughout this phase, the progeny of any given generation expressed arith- 

 metically must be greater than that of any previous generation. Lemon's method of 

 calculating the growth rate is likely to be of advantage in physiological and biochemical 

 problems when it is desired to study the rate of change in a chemical substrate in relation 

 to the absolute numbers of organisms produced. 



