464 Cell Penetration by Acids. IV 
For the utilization of the results of these penetration studies it was 
necessary to know something about the action of this acid upon the surface 
of cells; so experiments were made to determine its behavior with the tissue 
of Chromodoris zebra; the results throw some light upon the factors which 
may cause the apparent speed of penetration by different acids, as ob- 
served by this method, to vary in different tissues. 
II. The technique in these measurements of the penetration 
of o-phosphoric acid was essentially as has previously been 
explained (Crozier, 1916,a, 6). Some observations were repeated 
for certain acids giving penetration curves lying near that of 
phosphoric; these experiments sufficed to show that the curves 
previously published could be relied upon fdr comparison. Two 
series of experiments were made with phosphoric acid, at the same 
time but at different temperatures. The average penetration 
times obtained in the two series, as shown in Table I, differ to 
TABLE I. 
The apparent time required for the penetration of mantle tissue of 
Chromodoris by H;PO, at different concentrations and at two temperatures; 
penetration time in minutes; figures in brackets obtained only in favorable 
cases (about 75 per cent). 
Concentration, normal. 
Temperature. bs DR a ae) oe Sie es rae 
1.34 0.67 | 0.134 | 0.067 | 0.013 | 0.010 | 0.007 | 0.005 
HO min. min. min. min. min. min. 
24.8 220 4.2 ee Col 4114.3: 19120) oe o 
27.0 ey, Died, 4.9 6:0 1.13.0: 7518: Ole a 
a degree which will serve to illustrate the delicacy of the method 
(Fig.1). Observations were made at 27.0° and at 24.8°; the tem- 
perature of the sea water from which the chromodorids had been 
recently obtained was 24—25°. 
Ill. The average apparent penetration times of phosphoric 
acid, from different concentrations, are plotted in Fig. 2. It is 
seen that from low concentrations the penetration appears ab- 
normally slow, in comparison with some other acids; or that the 
increase in speed of penetration with higher concentrations is 
unusually rapid. From Fig. 2 it will be evident that at any par- 
ticular concentration ‘(e.g., 0.01 N) the apparent relative position 
of phosphoric acid in the series will depend upon the intensity of 
