2 10 
Brown. — Some Studies on Yeast . 
I have stated that the above relations do not hold good when the 
amount of seed-yeast falls much below i cell per unit volume. If the initial 
seeding is as low as o-i cell per unit volume, the departure from the above 
rule is very great. The explanation of this is to be found in the behaviour 
of the seed-yeast to the dissolved oxygen at the commencement. As we 
shall see a little later, the first action of the yeast, long before there are signs 
5 10 15 20 25 30 U 40 4-5 50 55 60 65 70 
' Time in houre 
Fig 5. Fermentations with limited supply of oxygen, and with varying initial amounts of seed- 
yeast, i7*o°C. A. Seed-yeast 0-93 cell per unit volume. B. 1-87 cells per unit volume. C. 2-8 cells 
per unit volume. 
of reproduction, is to absorb and fix the dissolved oxygen. This absorption 
is very rapid with a ‘ density of population ’ of yeast-cells equivalent to 
1 cell or more per unit volume, but with anything less than this the late of 
absorption falls off rapidly, and with anything like o-i cell per unit volume 
the absorption is so slow that sufficient time elapses to allow a more or less 
complete diffusion of the dissolved oxygen into the inert gas which replaces 
the air above the liquid. Under, these conditions reproduction is relatively 
