2 6 
Walter Stiles 
rate of increase of the electrical conductivity of the solution in the 
upper tube and the decrease in the conductivity of the solution in 
the lower tube was taken as a measure of the rate at which the salt 
or salts in the lower cell passed through the tissues, and therefore as 
a measure of the permeability of the tissue. To eliminate errors due 
to exosmosis from the cells and diffusion from the intercellular spaces 
of the tissue, control experiments were made in which the more dilute 
solution was contained in both upper and lower tubes. The average 
conductance of the solution in the upper tube of the controls at the 
end of the experiments was taken as the standard, and the average 
conductance of the solutions in the experimental tubes “divided by 
this figure in order to obtain the percentage which expresses their 
gain as compared with the control.” By this method it is stated 
that “the figures which were obtained in this manner measure 
the amount of salt which had passed through the tissue, while 
the errors due to exosmosis from the protoplasm as well as those 
due to diffusion from the intercellular substance are eliminated.” 
As disks of tissue vary in thickness, errors arising from this cause 
were eliminated by first performing an experiment with sea water 
and then using the same disk for an experiment with one of the salts 
examined. The rate of change of conductivity during the experiment 
with the salt solution was then divided by the rate of change in 
conductivity during the preliminary period when sea water was used. 
Experiments were also made with dead tissue. 
The principal objection that can be raised to this method is that 
there is no guarantee that the salt which diffuses into the cells on the 
lower side of the Laminaria thallus is the same salt which diffuses 
out from the cells on the upper side of the thallus. Possible combina¬ 
tions between salt and cell constituents are completely neglected. In 
short, the complexity of the system is disregarded, and the disk of 
tissue, several cells in thickness, is regarded as a simple membrane. 
How far this is justifiable is doubtful. 
The method has also been used to examine the permeability of 
cell walls, bulb scales of Allium being employed for this purpose 
(Brooks, 1917 c). 
