108 



PHYSIOLOGY OF BACTERIA 



is used up. There are various explanations for this 

 gradual retardation and ultimate cessation of the rate of 

 fermentation; it may be due to lack of substrate, or to 

 toxic action of fermentation products, or to some 

 biological change of the cells. While all these reasons 

 might occasionally fit, the common cause of the decrease 

 in rate ordinarily is either the accumulation of fermenta- 

 tion products, or the decrease of fermentable substrate. 



Table 



15. — Alcoholic Fermentation of Sugar Solutions of 

 Different Concentration by 5 Gm. of Yeast 



