1905.] 



The Alcoholic Ferment of Yeast-Juice. 



411 



in the reservoir at a fixed level, by means of a syphon dipping into a small 

 beaker. The volume of the gas was read on the azotometer without disturbing 

 the mercury reservoir and was reduced to atmospheric pressure by means of a 

 calibration curve. Since yeast-juice readily becomes supersaturated with 

 carbon dioxide, the contents of the flask were vigorously shaken before each 

 reading of the volume of gas. Before the observations were commenced the 

 liquids were brought to the temperature of the thermostat, and were saturated 

 with carbon dioxide. In all comparative experiments the concentration of 

 glucose was the same. 



When the rates of evolution of carbon dioxide from (1) a solution of glucose 

 in yeast-juice, and (2) a similar solution to which boiled and filtered yeast- 

 juice has been added are compared, it is found that two phenomena are- 

 concerned in the production of the increased fermentation in the presence of 

 boiled yeast-juice. 



(«) An initial rapid evolution of carbon dioxide is produced, which soon 

 diminishes until a rate is attained which remains nearly constant for several 

 hours and is usually, but not invariably, approximately equal to that given 

 by an equal volume of the same yeast-juice and glucose to which no addition 

 has been made. 



(b) The fermentation rate diminishes more slowly, so that the fermentation 

 continues for a longer period. The greater proportion of the total increase 

 is usually due to this second phenomenon. 



The results obtained in a typical experiment of this kind are shown in 

 Fig. 1. The initial period of the evolution is plotted separately (Curves A' 

 and B') on a larger scale. 



Curves A and A' in which the evolution of carbon dioxide is plotted 

 against time represent the course of a fermentation with 25 c.c. yeast-juice- 

 + 25 c.c. water +5 grammes glucose + toluene. The rate to begin with is 

 48 c.c. per hour, but rapidly decreases until it becomes equal to 24 c.c. per 

 hour, at which it remains almost constant for about 5 hours, gradually 

 decreasing until, after the expiration of about 40 to 45 hours, fermentation 

 ceases. The total evolution amounted to 369 c.c. under atmospheric 

 conditions. 



Curves B and B' refer to 25 c.c. of the same yeast-juice + 25 c.c. of a boiled 

 yeast-juice +5 grammes glucose + toluene. The initial rate is much higher, 

 168 c.c. per hour, but this falls gradually in the course of 40 minutes to 30 c.c 

 per hour. This rate of 30 c.c. per hour falls off much less rapidly than that 

 in Experiment A, the fermentation continuing for about 80 to 85 hours and 

 yielding in all 1174 c.c. of carbon dioxide. It is important to bear in mind 

 that these curves represent the gradual disappearance of the fermenting power 



