FOOD REQUIREMENTS 497 



maximal density of population might be decreased, with no appreciable 

 effect on the early growth rate (curve E). (5) The growth rate might 

 be decreased, without any effect on the maximal density of population 

 (curve F) . (6) Both the growth rate and the maximal density of popula- 

 tion might be decreased (curve G). These possibilities will serve as 

 illustrations. Curves A, B, and E would show no significant differences 

 in the early histories of the cultures; yet each reaches a different maximal 

 stationary phase, one higher and one lower than that of the control 

 (curve A). On the other hand, early examination of cultures A, C, and 

 F would show significant differences in population density and in growth 

 rate, although each culture eventually reaches the same maximal density. 

 Hence without detailed information concerning the behavior of popula- 

 tions, there is obvious need for caution in interpreting experimental 

 results. 



In an analysis of the conditions which might influence the population- 

 growth curve, the concentration of available food, the general condition 

 and density of the initial population, the pH of the medium, the tempera- 

 ture of incubation, the accumulation of waste products, the oxygen ten- 

 sion, and the redox potential of the medium — to mention some of the 

 more apparent factors — all seem to be significant. Although the impor- 

 tance of such factors may seem obvious, their detailed relationships to 

 growth are mostly unknown. 



The Initial Population 



Both the physiological condition and the size of the initial population 

 may influence the rate of growth. Phelps (1935) has reported that the 

 length of the initial stationary phase and the lag period bears a rela- 

 tion to the age of the inoculum. With inocula taken from the logarithmic- 

 growth phase of a stock culture, the length of the combined lag and 

 initial stationary phases was usually reduced to zero. With inocula from 

 older cultures, these two phases were usually detectable and were often 

 quite pronounced. Obviously, therefore, age and other qualities of the 

 inoculum must be considered in comparative studies on population growth 

 and on the effects of environmental factors. 



The relation between the initial density of population and the growth 

 rate in bacterized cultures has been disputed for many years. Robertson 

 and others have described an allelocatalytic effect, in which the rate of 



