214 
Brown . — Some Studies on Yeast. 
medium. In such cases diffusion can only become the limiting factor at 
very low outside concentrations, as shown by Slator for the fermentative 
faculty, and where diffusion ceases to limit the reaction there must always 
be a tendency to linear rather than logarithmic rate of change. 
If the water from which suspended yeast has absorbed all the dissolved 
ox yg en again saturated with air by strong agitation, the cells recommence 
their absorption at almost the same rate, and it is only by repeating such an 
experiment several times, or by passing strong currents of air through the 
Fig. 7. Curve showing the rectilinear rate of absorption of dissolved oxygen by yeast at 15 0 C. 
Liquid used was water saturated with atmospheric air. The values on the line of ordinates give the 
percentages of full saturation remaining, and measure the absorption of oxygen. Seed-yeast used : 
a. o-i grm. pressed yeast per 100 c.c. = 1 cell per unit volume. B. 0*2 grm. pressed yeast per 
100 c.c. = 2 cells per unit volume, c. 0*3 grm. pressed yeast per 100 c.c. = 3 cells per unit 
volume. 
liquid for an hour or two, that any marked diminution in the absorbing 
power is noticeable. 
The main facts which have been established experimentally, with 
regard to the reproduction of yeast-cells in a nutrient liquid containing 
dissolved oxygen, and an excess of all the mineral and organic substances 
requisite for their full nutrition, may be summarized as follows : 
1. When the available oxygen is limited to that initially contained in 
the liquid, the number of yeast-cells per unit volume tends to attain 
a maximum which is independent, or nearly so, of the number of cells of 
seed-yeast per unit volume, but is conditioned in the first instance by the 
initial amount of this dissolved oxygen. 
