222 PHYSIOLOGY OF BACTERIA 



with the increase of temperature, Table 58 represents 

 the temperature coefficients of B. ramosus computed 

 from Table 57, and those for Bad. coli obtained by- 

 Barber (1908). This relation is shown graphically in 

 Fig. 23. 



It should be mentioned that Barber in his direct microscopic 

 observations with Bad. coli made no statements indicating that he 

 ever found the Tammann principle. He never observed more 

 than ten generations, and the generation times were 



at 40°C. from 17-25 minutes 

 at 42°C. from 20-23 minutes 

 at 45°C. from 18-30 minutes 

 at 47°C. from 42-68 minutes 



with no differences whether ten or only two generations were observed. 



We had started with the assumption that the growth 

 rate is increased by temperature increases in the same 

 way as any chemical process, and that the deviations 

 at the maximum and minimum temperatures (as evi- 

 denced by Figs. 21 and 23) are to be explained by a 

 superposition of other factors. The existence of a true 

 optimum and a less definite maximum temperature for 

 the growth rate could be accounted for very satisfactorily 

 by the Tammann principle. The difficulty lies in 

 explaining the minimum temperature. 



Growth is the result of many interlinking processes. 

 If one of these many processes is extremely slow, the 

 entire growth is slow. If one of the processes ceases to 

 function, there will be no growth, regardless of the con- 

 dition of all other involved agencies. At the minimum 

 temperature, there is evidently some limiting factor, 

 but we have not sufficient knowledge of the growth 

 mechanism to locate this factor. 



