GROWTH CURVES OF BACTERIA 



Two principal types of explanation or interpretation have been used for the form 

 assumed by bacterial growth curves. The first of these (a succession of growth phases) 

 is the one developed above. In its essentials it was apparently first outlined by 

 Lane-Claypon/ and later expanded by the writer.^ A somewhat different method 

 of attack was suggested by McKendrick and Pai,^ and emphasized among others by 

 Robertson^ and Lotka\ These authors conclude that the sigmoid shape of the growth 

 curve is evidence of the resemblance of growth to the phenomenon of autocatalysis 



(or, in the terminology suggested by 

 Ostwald, "autocatakinesis"). While 

 these two interpretations are not 

 essentially antagonistic, they represent 

 somewhat different points of view, 

 and require separate treatment. 



GROWTH CURVES CONSIDERED AS A SUC- 

 CESSION OF GROWTH PHASES 



It was noted above that in some 

 cases at least as many as five different 

 growth phases may be observed in a 

 culture of bacteria. They will be con- 

 sidered in order. 



flnne in Hours 



Fig. 4. — Growth curve graphed as logarithms of 

 numbers of bacteria against time. 



a-h Initial stationary phase 



h-c Lag phase 



c-i Logarithmic phase 



d-e Phase of negative acceleration 



e-j Maximum stationary phase 



INITIAL STATIONARY PHASE 



During this phase there is no in-, 

 crease in numbers. In the illustration 

 above its existence was ascribed to the 

 time required for spores to germinate. 

 Experience shows, however, that this 

 phase is sometimes evident in a bac- 

 terial transfer although the organism is one which does not sporulate. It is apparent 

 that bacterial cells from old cultures (in the maximum stationary and later phases) 

 possess some of the same inertia and slowness to develop under favorable environ- 

 ment usually regarded as characteristic of spores. They may be regarded as in 

 some respects the physiological, though not the morphological, equivalents of endo- 

 spores. In some cases this phase may be prolonged for days or weeks. Such prolonga- 

 tion has been noted particularly by Esty and Meyer^ in heated cultures of the bacil- 

 lus of botulism. This phase is not found when the inoculum contains any considerable 

 proportion of actively multiplying bacteria. 



' Lane-Claypon, Janet E.: J . Hyg., 9, 239. 1909. 



" Buchanan, R. E.: /. Infect. Dis., 23, 109. 1918. 



3 McKendrick, A. G., and Pai, M. Kesave: Proc. Roy. Soc, Edinburgh, 31, 649. 1911. 



■t Robertson, T. B.: /. Physiol., 56, 404. 1922. 



sLotka, Alfred J.: Elements of Physical Biology. 1925. 



' Esty, J. R., and Meyer, K. F.: J. Infect. Dis., 31, 650. 1922. 



