GROWTH 



207 



In discussing growth, some authors do not distinguish sharply 

 between growth rate and numbers of cells. A small increase in the 

 growth rate will cause a conspicuous increase in total numbers if 

 the experiment extends over a long period. The faster growth 

 rate works all the time, and the results multiply and accumulate 

 similar to compound interest. 



Table 51. — Development op Strept. lactis in Skim Milk of Different 

 Concentrations 



Lactose concentration in %! 10 

 Milk concentration 2 X 



5 

 IX 



2.5 

 0.5 



1.250.6 

 0.250.125 



0.3 

 0.062 



0.15 10.075 

 0.03l!0.016 



Fermenting capacities X 10^" mg. 



Generation times in minutes 



Final number in millions of cells per c.c, 



36-48 hours 888 1468 725 307 223 130 0.93 1.0 



The rather incomplete data of Peltier's unpublished experiments 

 (see p. 118) may be given here as a summary. Skim milk powder 

 was dissolved in water to a concentration about twice the normal 

 concentration of milk. Of this concentrated milk, part was diluted 

 with an equal amount of water, giving skim milk of normal strength. 

 Part of this was diluted again with an equal amount of water, and 

 so on. The different dilutions were sterilized, inoculated with 

 Strept. lactis, and the bacteria were counted, and the acid titrated 

 frequently. From these data, the fermenting capacities and the 

 generation times were computed. Table 51 gives the averages of 

 there sets of experiments. 



