228 PHYSIOLOGY OF BACTERIA 



regenerated by the cell. This regeneration has a limited 

 speed. As long as the deterioration of the growth agent 

 does not exceed its regeneration, everything goes well, 

 and a stimulation up to this point will be well tolerated 

 by the cell. Beyond this point, cessation of growth is 

 inevitable if the stimulation continues. This deduction, 

 which is merely based on analogy, leads to the conclusion 

 that the Tammann principle should become evident 

 at higher concentrations of a chemical stimulant. 



Very little experimental evidence which includes the 

 time factor is available. A good example is an experi- 

 ment of Hline (1909) given in Table 61 which shows, 

 at first glance, a good agreement with the influence of 

 temperature on fermentation and on growth. It is a 

 fine illustration of the existence of the Tammann princi- 

 ple in chemical stimulation. 



This example may be objected to for the reason that the bacteria 

 are multiplying, and that, in the same culture, the same amount of 

 formaldehyde is acting upon much larger numbers of cells as the 

 time advances. However, the theory of stimulation by poisons 

 assumes that the action is catalytic, and therefore, its action is 

 independent of the concentration of the substrate i.e. the number of 

 cells. This assumption is justified because it will be shown on p. 341 

 that the death rate depends upon the concentration of the poison, 

 but is independent of the numbers of cells acted upon, within very 

 wide limits. 



The experiment quoted above is not sufficient, however, to make 

 any further deductions. There is a very long lag period, the control 

 requiring seven hours before the most rapid growth is reached. 

 Besides, the generation time of all cultures but the last shows a 

 distinct increase between two and four hours which suggests some 

 unknown outside retarding influence. Therefore, the generation 

 times mean little. 



All other material on growth stimulation refers to 

 final crops, and will be discussed later (p. 254). No 



