Brown. — Some Studies on Yeast. 
199 
B 
the ‘ rate of reproduction 5 — is in inverse proportion to the square root of 
the number of cells of the initial seed-yeast A. 
If this were strictly correct it follows that the value 
YA x B 
A 
B 
Y A 
On making 
should be constant for all the experiments in any one series. 1 
B 
the calculations it was found that the value for — 4 although not constant 
Y A 
for each series, nevertheless exhibited a general similarity, which is very 
remarkable when it is considered that the experiments from which they 
originate are concerned with the complex functions of living organisms 5 , 
and ‘ the relatively close agreement among so many experiments renders it 
very improbable that such a result has been obtained by mere chance 
Whilst my own work on this subject fully confirms that of Adrian 
Brown as regards the limitation of yeast-reproduction by deficient supply 
of free oxygen, I have found that under similar experimental conditions 
cell-multiplication stands in a much more simple relation to the time 
interval than is here stated, and this relation may be expressed as 
follows : — 
During the period of active reproduction of yeast in a suitable medium 
in which access of oxygen is limited to that initially present in sohition in the 
liquid^ the number of cells present at any moment is directly proportional to 
the time. 
If, for example, we denote the number of cells of the seed-yeast per 
unit volume by //, and the cell-count at any time during active reproduction 
by N, then when either N or N—n is plotted against the time, the result is 
a straight line, and the ‘ curve ’ only begins to depart from the rectilinear 
direction as the point of maximal cell-reproduction is reached. 
This fact is illustrated in the graphs of Fig. 1, in which Curve A repre- 
sents the results of one of my own experiments in which one cell per unit 
volume 2 of seed yeast was employed. Curve B shows the plotted results 
of a somewhat similar experiment described by Adrian Brown (Trans. 
Laboratory Club, 1890) in which the initial seeding was at the rate of 0*65 
cell per unit volume. Both sets of results illustrate the well-marked 
rectilinear character of the curves during the main period of cell-repro- 
duction, and the comparatively sudden change in their direction as the 
point of maximal cell-increase is approached. How far these curves depart 
from the logarithmic rate of increase is shown by the dotted line C, which 
gives the logarithmic curve of cell-increase for Experiment A, on the 
1 In the original paper (Journ. Chem. Soc., Trans., 1905, p. 1398) the above value, owing 
Y Ax B 
to a misprint, appears as - — — — • 
2 The unit volume referred to here and throughout the paper is c.mm. 
