R. E. BUCHANAN 



53 



Data of bacterial growth as studied by McKendrick and I'ai and by Lotka have 

 been found to conform measurably well to such autocatakinetic curves. Other cases 

 may be cited, however, in which the agreement is not good. This is particularly true 

 when there is manifested a prolonged initial stationary phase or lag phase. Then, too, 

 the rate of growth per cell may not be directly proportional to the concentration of 

 the available nutrients. Other factors may also alter the form of the growth curve, 

 and in consequence it may be unsymmetrical. The equations and relations of such 

 curves are more complex, and are not subject to ready analysis. Even if the data se- 

 cured are found to iit symmetrical curves, comparisons between curves secured under 

 varying environmental conditions are /? 

 not as readily made as between cor- 

 responding (particularly the logarith- 

 mic) growth phases. 



EFFECT OF AGE OF PARENT-CULTURE 

 UPON FORM OF GROWTH CURVES 



The work of Lane-Claypon {loc. 

 cit.) and others has shown quite clearly 

 that the phase of growth of the culture 

 from which a transfer is made influ- 

 ences markedly the form of the growth 

 curve in the daughter-culture. In most 

 cases the following results will be 

 secured: (i) Transfers from the initial 

 stationary phase will show a continua- 

 tion of this phase, followed by lag phase, etc., in normal sequence. (2) Transfers 

 from the lag phase will usually show a continuation of this phase, followed by the 

 logarithmic phase, etc., in normal sequence. (3) Transfers from the logarithmic phase 

 usually show a continuation of the logarithmic phase. In some cases allelocatalysis 

 (see below) may cause the culture to show an initial lag phase. (4) Transfers from the 

 phase of negative growth acceleration will usually show a lag phase. (5) Transfers 

 from the maximum stationary phase may show an initial stationary phase or a lag 

 phase. 



EFFECT OF SIZE OF INOCULUM UPON THE FORM OF THE GROWTH CURVE 



It has been shown by Robertson^ that growth in a subculture of certain organisms, 

 particularly protozoa, is stimulated by the presence of other cells of the same type. 

 Single-cell transplants to hanging drops exhibit a much slower initial rate of growth 

 per cell than do seedings of a larger number. This phenomenon of mutual or self- 

 stimulation he terms "allelocatalysis." Wliile in general results with bacteria do not 

 show this effect under the usual conditions of culture, there is evidence that with some 

 forms, as the pneumococcus, single-cell isolations are very difficult. The work of 

 Valley and Rettger^ and others seems to indicate that many organisms grow very 



' Robertson, T. B.: Biocliem. J ., 15, 595. 1915. 



^ Valley, George, and Rettger, Leo F.: J . Bad., 11, 78. 1926. 



Time 

 Fig. 6. — An autocatakinetic growth curve 



