Stiles and J 0rgemen. — Studies in Permeability . IV. 51 
a stoppered vessel and a definite amount of plant tissue is added. The 
vessel is kept at a constant temperature in a thermostat, and the electrical 
conductivity of the liquid measured at suitable intervals by Kohlrausch’s 
method. From the numbers obtained in this way the relation between time 
and exosmosis of electrolytes may be exhibited graphically in a curve. In 
the majority of our experiments we have used potato tissue. Cylinders of 
potato were cut out from the tuber by means of a cork-borer, and these were 
cut up into discs of a definite thickness. These discs had a diameter of 
17 mm., a thickness of about 1-75 mm., and a weight of about 0-45 grm. 
After they were prepared they were washed for an hour in running tap- 
water, rinsed rapidly in distilled water, and then dried with blotting-paper. 
In each experiment twenty discs were immersed in 50 c.c. of solution. The 
experiments were carried out at a constant temperature of 20° C., and the 
conductivity measurements were all made at the same temperature. 
In order to correct the results obtained for the depression in conductivity 
due to the presence of non-electrolytes in the solution, the following method 
was adopted. Thirty-six grm. of potato discs were boiled in about 95 c.c. 
of water and the extract so obtained made up to 100 c.c. This should give 
a solution of approximately double the strength of the external solutions 
when equilibrium is attained. Quantities of 10 c.c. of this were then taken and 
made up with either pure water or a solution of the non-electrolyte to 20 c.c. 
The conductivity of the solutions so obtained was measured, and by this 
means curves were obtained showing the depression of the conductivity 
brought about by various concentrations of the non-electrolytes employed. 
With lower concentrations of cell exudate the absolute decrease in con- 
ductivity resulting from the presence of non-electrolytes is smaller, the 
lowering being approximately proportional to the concentration of electro- 
lyte. These results agree with the extensive observations of Jones and his 
collaborators ( 5 ). By means of these curves the numbers actually obtained 
in the experiments were corrected before plotting the curves between the 
time and the exosmosis of electrolytes.- In the case of methyl, ethyl, and to 
a less extent propyl alcohol, where high concentrations of alcohol were used, 
the correction that has to be applied in this way is large (see Figs. 4 and 5), 
but in other cases, though it is much smaller, it is as well not to neglect it. 
As the discs are liable to vary in thickness and weight some experi- 
ments were made in which discs of various thickness and weight were used 
with the same quantity of external solution in each case. The liquid used was 
an aqueous molecular solution of pyridine ; in each case 50 c.c, of this 
solution were employed with twenty discs. The weights of the twenty 
discs in five cases were 3-8 grm., 4*1 grm., 5-8 grm., 9*4 grm., 14*74 grm. 
The curves given in Fig. 1 show the relation between the time and the 
exosmosis of electrolytes in the five cases. It will be noticed that in each 
case there is a rapid exosmosis of electrolytes lasting over the first few 
