152 PHYSIOLOGY OF BACTERIA 



data in Table 35 compiled from results by Orla-Jensen 

 (1919) in glucose peptone solution. There is an 

 increase in the endpoint with increasing temperature 

 up to a definite optimum, and beyond that a rapid 

 falling off. The question might be raised whether 

 four weeks' time is sufficient to obtain endpoints at 

 temperatures below 10°C. 



All experiments agree in this observation that at the optimum 

 temperature or above, the final concentration of fermentation prod- 

 ucts is not as high as at somewhat lower temperatures. The dis- 

 agreement of different experiments appears when we approach the 

 minimum temperature. In Table 34, 9°C. for yeast is considera- 

 bly above the minimum temperature of growth or fermentation while 

 in Marshall's and Orla-Jensen's data, the minimum has been nearly 

 or entirely reached. Both these series are rather unsatisfactory, 

 however, as they combine growth and fermentation. If growth is 

 very slow, the endpoint may not be reached in four weeks. 



Experiments with large numbers of cells are more 

 useful in the study of endpoints. Table 36 sum- 

 marizes the endpoints obtained with three strepto- 

 cocci by the author (see also p. 134). Evidently, 

 the endpoint does not increase continuously with 

 decreasing temperature. At — 1°C. where no growth 

 takes place, the cells ferment for a while, but the amount 

 of total acid remains very low. With strain 23, the 

 cells died slowly, with strain 18, more rapidly. The 

 reason for this low endpoint does not seem to lie in 

 the dying of the cells, nor in an accumulation of other 

 harmful compounds, for the same cultures, after four 

 to five weeks at — 1°C., produced 0.7-0.8% of acid 

 within forty-eight hours after being placed at 30°C. 



The situation of the fermentation at temperatures 

 below the growth-minimum appears to be this: The 

 cells are entirely normal at the start, having been grown 

 near their optimum temperature. Centrifugation and 



