208 
Brown . — Some Studies on Yeast . 
in nine such experiments with the same wort and the same seed-yeast, the 
conditions of cultivation in all cases being maintained constant with the 
exception of the degree of aeration, which is the only variable. The cell- 
increases per unit volume are indicated on the line of ordinates, whilst the 
intervals on the abscissa line show the percentages of fully aerated wort 
contained in the mixture. 
It will be noted that up to 65 or 70 per cent, of complete aeration the 
cell-increase is directly proportional to the available oxygen present in 
the culture medium at the commencement of growth, and that beyond this 
point further increments of oxygen produce a smaller and ultimately 
vanishing effect. 
In order to carry the argument further and to obtain the absolute values 
of the free oxygen involved in these experiments, we must know the ratio of 
the coefficient of solubility of atmospheric oxygen in malt-wort to that in 
water at the same temperature. If we denote the former value by c 1 and 
the latter by c , then the ratio ~ as given by Pasteur is about o*86 for 
a wort of sp. gr. 1*060. 
In a series of experiments on worts of sp. gr. 1*050, using the Adeney 
apparatus for pumping out the dissolved gases after complete saturation 
with air, I have found the ratio - = 0-82 at 16 0 C. 
J c 
According to Roscoe and Lunt, the solubility of atmospheric oxygen 
in water at 16 0 C. and 760 mm. pressure is 0-682 c.c. per 100 c.c. of water, 
so that a malt- wort of sp. gr. 1-050 when fully saturated with air should 
contain 0-682 xo-82 = 0-559 cc - °f oxygen per 100 c.c. 
From the curve of Fig. 4 we see that its course is almost exactly 
rectilinear up to 60 per cent, of oxygen saturation of the wort, that is to say 
that within these limits cell-increase is a linear function of the available free 
oxygen. 
This 60 per cent, of complete saturation is represented in absolute units 
by o-6o x 0-559 = 0-335 c.c. of oxygen per 100 c.c. The consumption of 
this amount of oxygen has resulted in the production of 11*0 — 6-4 = 4*6 
cells per unit volume of ^oVo c.mm., so that for the production of one 
cell per unit volume there has been used up per 100 c.c. an amount 
o- 02 x 
of oxygen represented by — - ~ = 0-07 
4*6 
c.c. But one cell per unit volume 
of 40V0 c.mm. is equivalent to 400 millions of cells per 100 c.c., so that each 
single cell of this aggregate has on an average required for its production 
the expenditure of 
7 x 10“ 
= 1*7 x io“ 10 c.c. of oxygen. 
4 x io c 
Now the average volume of a yeast-cell, assuming it to be a sphere 
of 8 /x in diameter, is 2*68 x io~ 10 c.c., so that the above-mentioned 
