Brown — Some Studies on Yeosi. 
209 
volume of oxygen requisite for the subdivision of one yeast-cell into two, 
when expressed as a fraction of the volume of the original cell, is 17 x io~ 10 
-r* 2*68 x io“ 10 = c *63. 
It will be noted from the curve of Fig. 4 that even after complete 
de-oxygenation of the culture medium there has been a cell-increase 
equivalent to about 6*5 cells from each single cell of the seed yeast. 
It might be supposed that this is due to a small amount of oxygen left 
in the liquid, or to its subsequent introduction by faulty manipulation. It 
is impossible, however, to accept this explanation, since similar results are 
obtained when extreme care is taken to eliminate these sources of error. 
It is no doubt a fact that the yeast-cell has a limited power of reproduction 
under strictly anaerobic conditions, owing, as we shall see later, to its 
power of storing up oxygen prior to the seeding process. 
We may now turn to the effects which variations in the amount 
of seed-yeast exert on cell-reproduction when all other conditions remain 
the same. 
Adrian Brown came to the conclusion that when the supply of free 
oxygen is constant, the cells increase up to a certain maximal amount 
per unit volume which remains constant even when the amount of seed-yeast 
varies considerably. 
With certain limitations this conclusion is no doubt approximately 
correct, especially when we compare the true values of the cell-increases 
N—11 instead of the final counts N, and care is taken that the available 
oxygen is strictly identical in the various experiments. In my own experi- 
ments this was ensured by arranging, in the manner already described, that 
the available free oxygen was confined to that dissolved in the culture-liquid, 
and that no further access of oxygen was possible at any subsequent stage. 
Under these conditions, and provided the seed-yeast does not fall 
below one cell per unit volume, not only is the maximal reproduction N—n 
constant, or nearly so, for considerable variations in the seeding, but during 
the reproductive stage the number of new cells formed in a given interval of 
time is also constant and independent of the rate of seeding. 
This is shown in Figs. 5 and 6. In Fig. 5 the results are given of three 
of my own experiments in which the seed-yeast amounted to 0*93, 1-87, 
and 2-8 cells per unit volume. 
Fig. 6 gives the curves which I have deduced from a series of Adrian 
Brown’s experiments, in which the cells of seed-yeast per unit volume 
initially amounted to 1-57, 2*35, and 3-14 respectively. 
The general parallelism of these curves bears out what has been said 
as to the progressive and final reproduction being independent of the 
original seeding. They are phenomena which might have been deduced 
from the fundamental fact that there is, within certain limits, a quantitative 
relation between cell-multiplication and the supply of free oxygen. 
