140 Microbes and You 



1. The latent or initial stationary phase, from 1 to 2 on the 

 growth curve, is a period during which there is no detectable in- 

 crease in the number of bacterial cells. In fact a few cells may 

 die due to lack of adjustment to their new environment. 



2. The lag phase, from 2 to 3, represents a period during which 

 the cells are beginning to show signs of multiplication. This lag 

 phase plus the initial stationary phase are combined by some per- 

 sons into what they prefer to call the adjustment period. 



The length of the lag phase can be altered in a number of ways, 

 A large inoculum, for instance, will usually shorten this period in 

 the growth curve, while spore-formers or bacteria transferred to 

 this fresh medium from another culture in its death phase will 

 tend to prolong the lag phase. Any deviation from the optimum 

 with respect to the temperature of incubation or the type of food 

 provided will influence the length of this adjustment phase in the 

 growth curve. 



It was discovered by Valley and Rettger that carbon dioxide 

 gas greatly influences the growth of bacteria. If this gas is com- 

 pletely removed from an otherwise ideal environment, growth of 

 organisms will cease. The reincorporation of even minute traces 

 of carbon dioxide promptly initiates growth once again. Perhaps 

 a heavy inoculum helps to provide enough of this vital gas to 

 shorten the lag phase of growth. 



3. The logarithmic phase, from 3 to 4, is that stage in the 

 growth cycle when multiplication of the cells is at its maximum 

 speed and is occurring at regular intervals. The increase in num- 

 bers of cells is in a geometric progression, and if the logarithms of 

 the numbers of cells are plotted against time, they will fall along 

 an ascending straight line. 



4. The negative acceleration phase, from 4 to 5, is the period 

 during which multiplication slows down and the straight ascending 

 line begins to bend to the right, indicating fewer cell divisions per 

 unit of time. 



5. The maximum stationanj phase, from 5 to 6, is a segment 

 during which the numbers of viable bacteria remain almost con- 



