Brown . — Some Studies on Yeast. 21 1 
slowed down and is no longer comparable with that observed for higher 
rates of seeding. 
Pasteur, in his * Etudes sur la biere \ describes certain experiments 
which he made to determine the rate at which free oxygen dissolved in 
malt-worts is absorbed by yeast, making use of the Schlitzenberger method 
for oxygen estimation. He gives the particulars of an experiment made in 
a brewery in which the free oxygen dissolved in a malt-wort was determined 
hour by hour after the addition of the yeast, the temperature being 6° C. 
n 
l 
5 10 15 20 25 30 35 40 
Tiim in hours 
Fig. 6. Plottings of three experiments of Adrian Brown (see Journ. Chem. Soc., 1905, p. 1398) 
showing final countings of yeast-cells after cultivation for seventeen hours, the initial seed-yeast being 
varied in amount. Curve A. Seed-yeast 1*57 cells per unit volume. Curve B. Seed-yeast 2-35 cells 
per unit volume. Curve c. Seed-yeast 3-14 cells per unit volume. 
From the particulars given of the amount of yeast used, it must have been 
equivalent to about 1 cell per unit volume of -zpoVo c.mm. The results 
which were plotted out show that within six hours the residual oxygenation 
had only about 25 per cent, of the initial value, and that at the end of twelve 
hours from the commencement all the dissolved oxygen had disappeared. 
With double the amount of yeast the free oxygen disappeared in less than 
half the time. Pasteur further states that when this free oxygen had been 
removed from the wort the yeast-cells still showed no signs of reproduction, 1 
but they had assumed a younger and fuller appearance, and he draws the 
1 It must be remembered that the yeast used in this experiment of Pasteur was a ‘ bottom 
yeast ’ which was functioning at a low temperature ; hence oxygen absorption and initial rate of 
reproduction were relatively slow. 
