176 



PHYSIOLOGY OF BACTERIA 



growth. We shall see later, from Claassen's data, that 

 about one-half of the yeast solids is non-protein in 

 nature. 



An interesting observation is the alcohol: CO2 ratio. This should 

 be according to the simple fermentation formula (p. 42), 1.04. 

 In the experiments without aeration, this ratio is a little higher, 



Table 38. — Balance Sheet op Yeast Growth 

 (All data are gm. per liter) 



Experiment number. 



Aerated 



II III 



Not aerated 



II 



Duration of experiment. 



Total carbon dioxide formed . 



Total alcohol formed 



Alcohol plus carbon dioxide. . 



Sugar used 



Sugar minus alcohol and CO 2. 

 Yeast growth 



8 



hours 

 11.39 



8.02 

 19.41 

 23.34 



3.93 



5.48 



24 



hours 

 14.78 



5.17 

 19.95 

 23.76 



3.81 



8.85 



28 



hours 



12.96 



4.83 



17.79 



17.96 



0.17 



6.73 



hours 

 6.58=* 

 8.00 

 14.58 

 19.01 

 4.43 

 2.40 



48 

 hours 

 7.03* 

 8.15 



15.18 



22.20 

 7.02 



(1.21)t 



* These CO2 values are too low. 



t This is the value for 6.75 hours; no later value is given. 



1.21 and 1.16, owing to an incomplete elimination of CO2 from the 

 wort. In the aerated experiments, it is much smaller, 0.70, 0.35 

 and 0.37 respectively. The reason for this is either the complete 

 oxidation of part of the sugar, or the utilization of alcohol by yeast, 

 or both. Doubtless, some alcohol is used by the yeast. In Expt. 

 II, all sugar had been used after the eighth hour; but during the next 

 sixteen hours, 5 gm. of alcohol per liter disappear, 1.25 gm. CO2 

 are produced and the yeast crop increases 2.5 gm. In Expt. Ill, 

 1.2 gm. alcohol are used after the eighth hour, together with the 

 remaining 0.3 gm. sugar, to produce 2.4 gm. of yeast and 3.0 gm. of 

 CO 2. Special experiments showed that yeast in sugar-free aerated 

 alcoholic solution with ammonium salts gained in weight 25 to 29 %, 

 while the alcohol decreased and CO2 was produced. 



