Permeability 251 
A curious phenomenon noted in the case of sulphuric acid is that 
in the lower concentrations the tissue actually absorbed water at 
more rapid a rate at first than in distilled water. Calculation of the 
probable error of experiment left no doubt that this is not to be 
accounted for on account of the variability of different samples of 
tissue. This phenomenon is rather difficult to account for, since as 
the concentration of acid external to the tissue is so low, the pene¬ 
tration of it into the cell sap could scarcely increase the osmotic 
pressure of the latter sufficiently to account for the increased rate 
of water absorption. It is possible that this increased swelling may 
be referred to the increased absorption of water by proteins and other 
colloidal systems in acid solutions as compared with distilled water, 
but definite evidence confirmatory of such a view is wanting. 
Thoday (1918 a) has shown that a similar increase of rate of 
water absorption in lower concentrations of the solute as compared 
with that in distilled water is to be observed in the case of osmic 
acid and mercuric chloride. It may be significant that mercuric 
chloride undergoes partial hydrolysis in solution so that the solution 
contains a small quantity of hydrochloric acid. 
5. Ethylic acetate and phenols 
The absorption of ethylic acetate by grains of barley was ex¬ 
amined by Brown and Worley (1912). Ethylic acetate enters the 
grain, but the rate of water intake is more rapid than from pure 
water. This was regarded by Brown and Worley at the time as 
possibly due to a simplification of the water molecule in presence of 
this ester. Later Brown and Tinker (1916 a) observed a similar 
phenomenon in the case of various phenolic solutions. Barley grains 
absorbed various solutions of phenol of different concentrations the 
more rapidly the more concentrated the solution. With a number of 
different phenols in half-normal concentration the rate of absorption 
was in this order: phenol, catechol, resorcinol, pyrogallol. The last 
entered at the same rate as water. Since variations in osmotic 
pressure, vapour pressure and viscosity of these various solutions 
are slight, while the rate of absorption is in inverse order to the 
surface tensions of the solutions (Worley, 1914), Brown and Worley 
conclude that surface tension is also a factor in determining the rate 
of entrance of solutions into barley grains. 
17—2 
