W. J. Crozier 469 
this point the inward diffusion of acid is very rapid, and the 
time for the observed effect is nearly proportional to the dilution 
of the acid. It may be stated here that the temperature co- 
efficient of penetration speed, for this latter portion of the curves, 
is of the order Qio = 2.0, indicating the chemical nature of the 
principal factor governing the penetration (as might be ex- 
pected). The coagulative action of HzPO, is so great that the 
resistance to subsequent diffusion is overcome only very slowly 
until a high concentration of the acid is used. From these facts 
it may be inferred that the primary action of the H;PQ, is more 
intense than that, eg., of HCl (at equal concentration). If 
comparison is made at’a point in the reduced data (Fig. 3) where 
the C,. = 0.01 N, it will be noticed that the H3PO, is slightly 
more active than HCl. These considerations explain why the 
apparent speed of penetration of H3;PO, from higher concentra- 
tions gives a more correct idea of the primary effect of this acid 
upon the tissue used; this is not the case with some other acids. 
SUMMARY. 
V. The relative apparent speed with which H;PO, penetrates 
different tissues is conspicuously modified by the density of the 
cells concerned, and by the proportion of ‘buffer’? substances 
present. When the gross observations of apparent penetration 
time are corrected by consideration of the limiting concentration 
of acid inducing visible color change, it is found that the obser- 
vations for each acid fall upon two intersecting curves of the form: 
1 L 
—— = k (concentration’)n 
ee ( ) 
which does not, however, have reference to adsorption. With 
mantle tissue of Chromodoris the coagulative action of H3PO,:is 
so pronounced that a relatively high concentration must be used 
before there is marked acceleration in the speed with which the 
quantity of acid sufficient to react with the indicator is forced 
to diffuse into the tissue. The primary (surface) action of H3PO, 
is greater than is made evident by its apparent penetrating power, 
and is also (probably) somewhat greater than its hydrogen ioni- 
zation would demand. 
AGAR’S ISLAND, BERMUDA. 
