Hind. — Studies in Permeability. III. 233 
concentration, as has already been shown in the second paper of this 
series (13). 
The experiments recorded in which the electrometric method of 
measurement was used show that an actual absorption of hydrogen ions 
does take place with all the acids examined. With the mineral acids on 
the one hand, and the fatty acids on the other, there is, however, a very 
noteworthy difference. In the case of the former there was a continuous 
absorption of acid as far as the experiments were carried ; with the latter 
this continued reduction of the acidity of the external solution gave place 
after a time to a marked increase in the acidity. A discussion of this result 
follows later in this paper. 
II. Experiments with Living Plants of Vicia Faba. 
In order to determine whether the roots of living plants absorb acids 
in a similar way to potato cells, some experiments were made with Bean 
plants ( Vicia Faba). Seeds were germinated in sawdust, and the young 
seedlings transferred to water-culture solutions, so that the roots of the 
experimental plants should be uninjured. Before an experiment the roots 
of the plants were well washed with distilled water, then the plants were 
placed with their roots in bottles containing 100 c.c. of acid. 
N 
Series 11. In this series, Bean plants were used with nitric acid. 
r 1000 
Both the conductivity and the hydrogen-ion concentrations of solutions 
were measured after various intervals. Fig. 10 shows the change in 
conductivity, and Fig. 11 the rate of absorption of the hydrogen ion. 
These results indicate that the absorption of acid by living Bean 
plants takes place in exactly the same way as the absorption by discs of 
potato tuber. 
III. On the Part played by proteins in the Absorption of 
Acids by Potato Cells. 
In order to obtain some information as to which of the various sub- 
stances present in the cells of the potato are responsible for this rapid 
absorption of hydrogen ions, potatoes were ground up with sand and 
subjected to pressure. The expressed liquid so obtained was filtered off. 
The filtrate contained sugar and proteins, but no starch. The hydrogen- 
ion concentration of the liquid was measured, and was found to be only 
slight. 
N 
There was now added to 100 c.c. of an acid solution 1 c.c. of the 
1000 
filtrate, and the hydrogen-ion concentration of the resulting liquid measured. 
The hydrogen-ion concentration had decreased considerably. An attempt 
