Permeability 155 
contraction of the protoplast from the cell wall also takes place, but 
the vacuole contracts much more so that the width of the protoplast 
may increase greatly at the expense of the vacuole. 
Osterhout offers two possible explanations of this observation. 
Firstly, the outer surface of the protoplasm may be more permeable 
to ammonium chloride than the inner, or secondly, the ammonium 
chloride may produce an alteration in the permeability which causes 
a contraction called “false plasmolysis 1 .” If this false plasmolysis of 
the inner surface is greater than that of the outer, the observed 
effect would result. 
This observation may, of course, be truly explained on the basis 
of semi-permeable membranes surrounding both the protoplasm and 
the vacuole, but it might also be explained by supposing that the 
ammonium chloride altered the swelling capacity of the protoplasm 
as a result of which it absorbed water from the vacuole with the 
observed result. 
5. Evidence derived from a Consideration of the Electrical 
Conductivity of Living Cells and Tissues 
Living cells and tissues have a remarkably high electrical resist¬ 
ance (Stewart, 1897; M'Clendon, 1910), which rapidly falls if the 
cells or tissues are treated with a reagent bringing about the death 
of the cells (Osterhout, 19126; Stiles and Jorgensen, 1914 a). This 
phenomenon is easily explained by supposing that in the living cell 
the plasma-membrane offers considerable resistance to the passage 
of ions across it, but that when the cell is killed the organisation of 
the plasma-membrane is altered so that it becomes readily permeable 
to ions. That a visible change does often take place in the surface 
layer of the cell at death has already been noted. 
Other explanations of these phenomena are however possible. 
Thus if electrolytes in the cell were held in molecular association 
with the cell colloids there would exist a system of high electrical 
resistance, while death of the cell might involve a breaking down 
of these compounds and the setting free of electrolytes. How¬ 
ever, Hober (1910, 1912 b, 1913) has shown by ingenious electrical 
methods that free electrolytes are present in the cells of red blood 
corpuscles. 
1 Such a contraction has been noted by Osterhout (1908 a, 1913 c) when 
cells are immersed in dilute solutions of various salts or even in distilled water. 
This evidently has nothing to do with true plasmolysis. 
