Stiles a?id j0rgensen . — Studies in Permeability. V ’ 427 
Shrinkage then commences and continues for at least sixteen hours, after 
which time the tissue may have lost in weight by about 20 per cent. (Fig. 8). 
In higher strengths than 2 M the preliminary swelling phase is reduced, 
and in solutions of 5 M and 10 M shrinkage is considerable after half an 
hour. It is clear that the higher the concentration of alcohol the more, 
rapid is the rate of shrinkage. 
With concentrations less than iM the preliminary swelling period is more 
marked. Thus, in a gram-molecular solution maximum swelling is reached 
after about ten hours and is a higher value than the maximum swelling in 
M 
the case of a 2 M solution. With — ethyl alcohol the maximum is not 
reached even after sixteen hours, nevertheless the swelling is lower than in 
distilled water. 
The explanation of these phenomena on the membrane hypothesis is 
simple. Ethyl alcohol is supposed to penetrate the membrane, and in so 
doing to alter its constitution in such a way that it becomes permeable to 
the dissolved substances inside the cell. In the first stage of the process, 
therefore, the rise in osmotic pressure inside the cell owing to the addition 
of the alcohol produces swelling in what would have been hypertonic 
solutions if the alcohol had not passed through. If the membrane remained 
unaltered the cell should ultimately swell as much as in distilled water, 
provided no reactions took place between the alcohol and cell contents. 
But if the membrane is rendered more permeable to the solutes dissolved in 
the cell sap, these will diffuse out of the cell, slowly at first, then more 
rapidly as more of the membrane is changed, and finally more slowly again 
as the difference in concentration inside and outside of the cell becomes 
small. The exosmosis of the dissolved substances reduces the osmotic 
pressure inside the cell, which therefore loses water to the external medium. 
As the destruction of the membrane will take place more rapidly the higher 
the concentration of the alcohol, the exosmosis from the cell, and con- 
sequently the shrinkage, will be more rapid the higher the concentration. 
The curves given in Fig. 8 show that this is exactly what actually occurs. 
Moreover, that the exosmosis of dissolved substances takes place as 
this explanation supposes, has already been shown in regard to electrolytes 
in the preceding paper in this series ( 16 ). Reference may be made to the 
series of curves obtained for ethyl alcohol given in Fig. 6 of that paper, in 
which the exosmosis of electrolytes from potato tissue immersed in various 
strengths of ethyl alcohol is shown. It will be observed how exactly the 
exosmosis curves and swelling curves correspond. 
It is thus necessary to distinguish between the shrinkage due to 
plasmolysis and that due to injury. So Osterhout (11) distinguishes 
between true and false plasmolysis, the latter being the shrinkage which 
results from injury. 
Gg 
