Brown . — Some Studies on Yeast. 
219 
The immediate experimental data on which this result was founded 
consist of a determination of the actual amount of sugar fermented within 
short intervals of time corresponding to a rise of temperature of the liquid 
of from one to two degrees centigrade. 
In order to refer the rise of temperature to a definite weight or number 
of yeast-cells in a given volume of the liquid, a series of cell-countings were 
made at the beginning and end of each time-interval, by means of the 
haemocytometer. If the observations were made at a time when cell- 
reproduction had ceased, the initial and final countings were, of course, 
practically identical, but in those cases in which the ‘ oxygen charge’ had 
still not spent itself and the yeast was still reproducing, the arithmetical 
mean of the initial and final countings was taken as representing the average 
number of cells actively engaged in fermentation within the period. 
The actual amount of maltose which had disappeared during each 
period of observation was determined from accurate estimations of the 
alcohol produced, and from these data were obtained the weights of maltose 
which had disappeared from 100 c.c. of the liquid in one hour, under the 
influence of a definite number of yeast-cells per unit volume of the 
liquid. 
For convenience in further calculations and comparisons, this last value 
was further reduced so as to represent the weight of maltose per 100 c.c., 
which in one hour would have been fermented by a definite unit weight of 
yeast, or by a definite distribution of so many cells per unit volume, on the 
assumption (capable of proof) that under fixed conditions the amount of 
sugar fermented is proportional to the yeast present. 
A convenient standard to take for the yeast-distribution is that of 
10 cells per unit volume of c.mm., corresponding to 4 x io 9 cells per 
100 c.c. This number of cells weighs, on an average, 1 grm. 1 
If, in any such given case, we take M to denote the weight of maltose 
fermented per 100 c.c. per gramme of yeast (10 cells per unit volume) per 
hour; c the calories liberated by the fermentation of 1 grm. of maltose; 
and ^ the specific heat of the yeast-cell, which may be taken as approxi- 
mately o-86 ; then, assuming all conditions constant, the potential increase 
of temperature of the cell, if all the liberated energy of metabolism were 
retained in it, is represented by • 
In the following Table is given a summary of the results of ten experi- 
ments, from which have been calculated in the last two columns the time 
required for a yeast-cell under stated conditions of temperature to ferment 
1 This can be shown by washing a freshly cultivated yeast with water and then freeing it as far 
as possible from adhering moisture, either by repeated pressing between folds of filter paper or by 
distributing it over the surface of a porous tile. When one gramme of a top-fermentation yeast so 
prepared is thoroughly mixed with water and made up to 100 c.c. the cell-count per unit volume of 
4^00 c.mm. varies very little from ten. 
