Permeability 
27 
14. The Determination of Permeability to Dissolved 
Substances by Measurement of the Electrical 
Conductivity of Living Tissues 
A method for the measurement of the electrical conductivity of 
living tissues has been elaborated by Osterhout (1912#, 1913 a, 1914 j, 
1918 c, 1921) who regards the electrical conductivity of a tissue as 
a measure of the permeability of the protoplasm. Most of Osterhout’s 
measurements have been made with Laminaria thallus, but in the 
latest of the papers cited above apparatus is described suitable for 
use with other tissue, while a few experiments have been made with 
animal tissue (1919 c). The experimental material most usually em¬ 
ployed consisted of a pile of about 80 to 200 circular disks cut from 
the thallus of Laminaria Agardhii and arranged to form a cylinder 
like a pile of coins, the column of disks being kept in position by 
means of glass rods. At each end of the cylinder, and separated from 
it by a small length of solution, was a platinum electrode coated with 
platinum black contained in an electrode holder of hard rubber. The 
measurements of electrical conductivity were made by means of 
KohlrausclTs method. 
The question at once arises how far the electrical conductivity of 
tissue is a measure of the permeability of the protoplasm contained 
in its cells. This question has been discussed by Stiles and Jorgensen 
(1918) who have pointed out various difficulties which stand in the 
way of accepting the electrical conductivity as an exact measure of 
permeability. The electrical conductivity of a piece of tissue will 
depend on the conductivity of a number of different phases in the 
tissue, and we must consider the possible changes in all these phases 
when the conductivity alters. An increase in conductivity of living 
tissue is interpreted by Osterhout as an increase in the permeability 
of the protoplasm to ions. Now an increase in conductivity could be 
brought about in a number of ways apart from an alteration in the 
permeability of the protoplasm. Thus a change in the state of aggre¬ 
gation of the contents of the cell wall by which the content or nature 
of electrolytes was altered, as, for example, by diffusion or by breaking 
down of complex compounds, would alter the conductivity. This is 
by no means to be ruled out as a possibility having regard to the com¬ 
plexity of the cell wall (cf. Chapter VII). Experiments with dead 
tissue (cf. Osterhout, 1918 a) in which it is shown that dead tissue 
behaves differently from living tissue are not convincing evidence 
that the changes observed in living tissue are not in any way con- 
