230 ■ PHYSIOLOGY OF BACTERIA 



further data concerning the stimulation of the rate of 

 growth are known to the author. 



SUMMARY 



The rate of growth can be increased by certain 

 concentrations of chemical poisons. 



If a number of different concentrations are tried, 

 stimulation is greatest at first with the higher concentra- 

 tions, but the optimal stimulating concentration becomes 

 smaller and smaller as the time passes. 



This behavior suggests that poisons effect organisms 

 similarly as high temperatures, accelerating catalytically 

 the rate of action, as well as that of deterioration of 

 some essential growth factors. 



IV. THE ENDPOINT OF GROWTH 



All growth in a given amount of medium will ulti- 

 mately come to an end. The final amount of growth, 

 i.e., the total crop, will depend upon numerous factors. 

 With the same organism in the same medium, it will be 

 proportional to the volume of the medium (unless the 

 volume has had an influence upon the rate of oxygen 

 penetration into the medium). It will be independent 

 of the size of the inoculum unless this has been very 

 near to or above the number of cells that could develop 

 in the medium. (Rahn, 1906; Graham-Smith, 1920; 

 Buchanan and Fulmer, 1928.) 



The composition of the medium will have the greatest 

 influence. In our standard media, we are likely to get 

 quite uniform crops. It is generally considered a rule 

 that most of the common saprophytic bacteria, the 

 organisms of the colon-group, the streptococci (if sugar 

 is present) and quite a large number of other parasites 



