Brown — Some Studies on ■ Yeast. 205 
experiments, it may well become the paramount factor under another set of 
conditions. If, for instance, a rapid stream of air is urged through the 
culture liquid, and due regard is paid to keeping up the necessary food 
supply, then cell-reproduction is essentially controlled and limited by the 
alcohol factor. 
In order to investigate more fully the relation between oxygen supply 
and cell-increase, a further series of experiments was instituted on an 
entirely different plan. The general idea underlying these was to cultivate 
the yeast in a medium containing variable but known amounts of oxygen, 
Fig. 2. Yeast cultivations with limited oxygen supply and varying amounts of added alcohol. 
Temperatures C. Seed-yeast i c.cm. per unit volume (=o*i gramme pressed yeast per 
100 c.c.) N.B. The figures in small circles denote total percentage of alcohol. 
and to express the final reproduction In each case as a function of the 
available free oxygen. 
Malt-wort was again the medium chosen for the cultivations. A flask 
of about four litres capacity was fitted up as shown in Fig. 3. This was filled 
to about two-thirds of its capacity v/ith malt-wort, which was then boiled 
rapidly for an hour or an hour and a half while a constant stream of 
hydrogen was passed Into the flask through tube A, escaping through c, 
the pinchcock B being at first closed. At the close of the boiling process 
some of the wort was forced into tube B by closing c. B was then again 
closed and C reopened, the flask and its contents being allowed to cool 
whilst the stream of hydrogen was still passing. This de-oxygenated wort 
could then be passed over by hydrogen pressure into a series of cultivation 
