Permeability 211 
However, investigations of Stoklasa (1911) and others, and par¬ 
ticularly the critical research of Sziics (1913) on this subject, indicate 
that this explanation is not correct, for if it were, the following con¬ 
sequences should result. 
1. Cells plasmolysed in a hypertonic solution should become de- 
plasmolysed after addition of an aluminium salt to the external 
solution. 
2. The increased permeability of the protoplasm should con¬ 
dition increased exosmosis and consequent loss of turgor. 
3. As they can enter the cell more rapidly, toxic substances ought 
to exhibit their effects more rapidly in presence of aluminium salts. 
4. Substances which are microscopically recognisable ought to be 
clearly discernible by microchemical tests if they enter the cell in 
such amount that plasmolysis is prevented. 
5. The rapid entrance of strong solutions ought to have toxic 
effects which would condition exosmosis. 
Sziics could observe none of these consequences of Fluri’s theory 
of the action of aluminium ions. On the contrary, he found by 
centrifuging filaments of Spirogyra treated with an aluminium salt, 
that the action of aluminium ions is to fix the protoplasts, which 
remain in position under this treatment, while normal living proto¬ 
plasts collect in the ends of their cells. Aluminium chloride, sulphate, 
nitrate and acetate all appear to behave in the same way, while 
yttrium and lanthanum salts also appear to have the same action. 
On returning the cells after treatment to water, they recover their 
original state. There is no doubt that the effect is reversible. If the 
aluminium ion is allowed to act for a longer time, and if it is in 
sufficient concentration, the protoplast becomes "loosened” again, 
and then collects in the ends of the cell on centrifuging, in the same 
way as in a normal living cell. The fixing action can be observed in 
Spirogyra immersed for only a minute in a solution of aluminium 
nitrate as dilute as 0-0064 The greater the concentration the more 
rapidly both the fixing action and the subsequent "loosening” take 
place. It should be noted that aluminium ions do not exert this 
fixing action on anthocyanin-containing cells of a number of different 
species examined by Sziics. 
Harvey (1911, 1913), from experiments in which cells were first 
impregnated with neutral red (cf. Chapter xi), concluded that sodium 
hydroxide does not readily enter cells of Elodea , Spirogyra , Para¬ 
mecium and eggs of various echinoderms, but that sodium salts in 
the external solution render the cell permeable to sodium hydroxide. 
14—2 
