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Walter Stiles 
that is, by determining the limiting concentration of sodium nitrate 
and potassium chloride required to produce plasmolysis of these cells 
after the lapse of different periods of time. Assuming the legitimacy 
of the method, which is doubtful, it was found that injury decreased 
the rate of intake of the salts employed for plasmolysis, whence it 
is concluded that wounding decreases the permeability of the proto¬ 
plasm of these cells to the salts in question. 
Seasonal Changes in Permeability 
Fitting (1915) found by the deplasmolytic method used by him, 
that salts were absorbed by the cells of the leaves of Rhceo discolor 
much more slowly in winter than in summer; he found the same thing 
with glycerol (1919). 
It is evident from what has already been written that the cell 
may vary under different conditions with regard to its capacity for 
absorbing or excreting both water and dissolved substances. In the 
case of the vacuolated cell such changes in the rate of the passage 
of water from external liquid to vacuole or vice versa may, with con¬ 
stant difference in osmotic concentration of the internal and external 
liquids, be regarded as due to changes in the permeability of the cell 
membranes (cell wall + protoplast) to water, although even this rests 
on the assumption of the complete correctness of the simple osmotic 
view of the plant cell, which has already been shown to be inadequate 
(cf. Chapter ix). 
The question of changes in permeability to dissolved substances 
is a much more difficult one. That changes in permeability are spoken 
of at all in this connexion is due to the acceptance of the membrane 
theory, and it must not be forgotten that other explanations are 
possible which do not involve passage of substances through a mem¬ 
brane (Moore and Roaf, 1908). With regard to the irreversible changes 
in permeability leading to the death of the cell, Szucs (1912) is of 
opinion that the so-called “increase in permeability ” brought about 
by narcotics and other compounds, and indicated by exosmosis of 
tannin from plant cells and the pigment from red blood corpuscles, 
has nothing to do with permeability because the phenomena observed 
are not connected with vital processes but are due to post-mortal 
changes. 
Yet even if the exosmosis resulting from the action of toxic sub¬ 
stances is not in the first place attributable to post-mortal changes. 
