566 
S. C. BROOKS 
In order to obtain figures for the different groups of salts which 
would be comparable with one another, it was necessary to correct 
for the difference between the concentration changes used for these 
groups. An empirical expression of the rate of penetration of a salt 
may be obtained by dividing the concentration change causing the 
decrease in curvature by the time in minutes required to regain the 
initial curvature, or, as we have termed it, the "recovery time." 
10 to }0 50 JO yo rjinate^. 
Fig. 2 
If such figures be used as the ordinates, and as abscissae the time elapsed 
between the first immersion of the tissue in the solution and the middle 
of the recovery time, there will be prodliced a curve expressing the 
permeability of the cells after any given period of exposure to the 
action of a salt. Such curves are shown in Figure 2. 
