200 
Brown. — Some Studies on Yeast. 
assumption that the successive doublings of the cell-counts had occupied 
equal intervals of time. 
There can be no doubt that the departure from the logarithmic rate in 
experiments of this kind indicates the existence of some restricting agency 
which exercises an influence even in the very earliest stages of cell-growth, 
but it must be one of an exceptional and peculiar nature to account for 
J 10 1 5 20 Z5 30 35 40 45 30 55 60 6 5 70 
Time in boors 
Fig. i. The figures in small circles denote alcohol percentages for Curve B. 
the rate of cell-reproduction being so consistently proportional to the time. 
That mere overcrowding of the cells suffices to account for the result is 
extremely improbable from the following considerations. 
In Experiment A (Fig. i) the seed-yeast amounted to one cell per unit 
volume of ^oVo c.mm., the average diameter of a yeast-cell (assumed to be 
spherical) being o*co8 mm. If we imagine the unit volume of liquid and its 
contained yeast-cell to be magnified a little over 1,587 diameters the unit 
volume will be represented by a cubic decimetre, and the yeast-cell by 
