R. E. BUCHANAN 



47 



These facts and relationships may be shown graphically in several ways. The 

 standard growth curve such as that noted above may be graphed (Fig. i) by plotting 

 numbers of bacteria against time. In- 

 spection of the graph shows the ex- 

 istence of some four readily differen- 

 tiable phases; the distinction between 

 the lag phase and the logarithmic phase 

 is not easily made by examination of 

 this type of curve. 



A second method of representing 

 increase in numbers is to plot the total 

 increase in numbers of bacteria in each 

 equal interval of time against time, 

 thus developing a "rate curve." Such 

 a curve corresponding to the growth 

 curve of Figure i is given in Figure 2. 



A third type of graph may also be 

 used to illustrate growth rates: one in 

 which the successive rates of increase 

 per cell (or, conversely, the generation 



Fig. 2. — Rate 

 curve of Fig. i. 



Time in Hours 

 curve corresponding to growth 



time) may be plotted against time. 

 Curves such as those in Figure 3 may 

 be thus secured. In this graph the 

 identification of the five growth phases 

 is more readily accomplished than in 

 Figures i and 2. 



A still clearer differentiation of the 

 various growth phases is to be secured 

 by a fourth type of graph in which the 

 logarithms of the numbers of bacteria 

 are plotted against time, as in Figure 

 4. During the initial stationary phase 

 (a-6) a straight line with o slope is 

 developed, during the lag phase (&-c) 

 a curved line, during the logarithmic 

 phase a straight line {c-d) with posi- 

 tive slope; during the phase of nega- 

 tive acceleration a curved line {d~e), 

 and finally during the maximum 

 stationary phase (e-/) a straight line 

 of o slope. 



A study of the typical growth curve 

 (Fig. i) shows it to be more or less 

 S-shaped. Its exact form in each case will depend upon the type of organism, its 

 immediately antecedent history, and the various environmental influences. 



13 20 JZ2 2^ 



'? c e JO 12 14 I 



Time in Houns 



Fig. 3 



A . Graph of rate of growth per cell 



B. Graph of generation times 

 a-h Initial stationary phase 

 h-c Lag phase 



c-i Logarithmic phase 



d~e Phase of negative acceleration 



c~j Maximum stationary phase 



