Brown . — Some Studies on Yeast . 
215 
2. Within certain limits of oxygen supply, the maximal reproduction is 
strictly proportional to the initial amount of this oxygen. 
3. The rate of reproduction under these conditions is not logarithmic, 
but is a linear function of the time. 
4. The dissolved oxygen does not remain as such in the liquid during 
the reproductive period, but is rapidly absorbed by the seed-yeast before 
cell-budding commences. 
A due consideration of the important fact mentioned in (4), and of 
everything which it implies, enables us to give a satisfactory explanation of 
all the phenomena we are dealing with. 
Although the main controlling influence on cell-reproduction is due to 
the free oxygen originally present in the nutrient liquid, this oxygen is 
absorbed very rapidly by the seed-yeast, the subsequent reproduction of 
which is brought about under conditions which, as regards the liquid itself, 
are anaerobic. We must therefore regard the potentiality of reproduction 
as being impressed on the cell at the very outset by the oxygen which it 
has absorbed, and that a quantitative relation exists between this absorbed 
oxygen and the number of subdivisions which the initial yeast-cells can 
finally make. The action is, in fact, one of indtiction , and all the known 
facts can be explained if we assume the equal partition of the available 
oxygen between the initial cells, and the consequent variability of the 
oxygen charge which these cells must receive when the ratio of the seed-yeast 
to the available oxygen varies. 
In order to illustrate this point, let us consider three hypothetical cases, 
A, B, and C, in which we have a nutrient liquid such as a malt-wort, 
saturated with atmospheric air, and therefore containing about 0*5 c.c. of 
dissolved oxygen per 100 c.c. We will assume that A is seeded with 1 cell 
of yeast per unit volume, B with 2 cells, and C with 4 cells, 1 and that 
further access of oxygen is prevented during the reproductive period. Under 
such conditions we should expect to find, at the termination of the repro- 
ductive period, about 16 cells per unit volume in each case, the final cell- 
count being independent, or nearly so, of the rate of seeding. This result 
can be explained as follows : In all three cases the dissolved oxygen is 
absorbed withfn a short time by the seed-yeast, but it is manifest that, when 
this has taken place, the initial oxygen charges of the individual cells in 
A, B, and C respectively must vary inversely as the original cell-countings, 
and will therefore be represented by the ratios 1 : \ : 
Since, within the limits of our experiment, the maximal cell reproduc- 
tion is known to be proportional to the oxygen supply, the number of 
possible cell-divisions of any individual cell in B will only be one-half of that 
in A, but since the initial number of cells in B is double that of A, the final 
1 These seedings approximately represent volumes of yeast-cells equivalent to o*i, o*2, and 
0-4 c.c. per 100 c.c. of liquid. 
