The Plasmatic Membrane. 
■»5 
All specific poisons which kill the cell cause, naturally, exos¬ 
mosis, but a large number of organic substances which are not 
specific poisons, such as alcohols, esters, etc., cause exosmosis in 
sufficient concentration. 
In a homologous series like the monovalent alcohols the critical 
concentration required diminishes rapidly as the series is ascended : 
methyl alcohol, 15%; ethyl, 10%; propyl, 4-5%; butyl, 1-2%; 
amyl, 0 5%. 
Now Traube, in 1904, got together evidence to show that the 
toxicity of these subtances increased in this way for animal tissues 
and that the effect of the different homologues in lowering surface- 
tension increases exactly pari passu. Each successive member of 
the series becomes three times as toxic and three times as depres¬ 
sant of the surface-tension when dissolved in water. It therefore 
looks as if the production of exosmosis is closely correlated with 
surface-tension of the liquid in which the cell is bathed. 
Czapek subsequently proceeded to determine the surface- 
tension of a great variety of organic substances in solution, and at 
the same time try their effect as producers of exosmosis. 
He determined the surface-tension in the simplest way by 
seeing what resistance the liquid offered to the formation of air- 
bubbles on pressing air through a capillary tube submerged in 
the solution. The head of pressure required to cause bubbles 
just to escape from the mouth of the capillary tube of his “capil¬ 
larity-manometer” gives a measure of the relative surface-tension 
of the solution employed. 
The correlation between surface-tension and exosmosis was 
most striking and unexpected, for it was found that if any organic 
substance whatever is dissolved in water in sufficient amount to 
lower the surface-tension to 0'68 (pure water being taken as unity) 
then this solution just brings about exosmosis from the cell. There is 
thus established a new principle of great fundamental importance. 
The cell’s power of retaining its contents is a matter of physical 
organisation of the superficial layer, and these substances which 
upset the power do so, not by virtue of any chemical action on the 
protoplasm, but by some surface-tension relation. 
Specific poisons, which cause exosmosis in much weaker con¬ 
centrations no doubt act chemically on protoplasm (and indeed 
many of these do not lower, but raise, surface-tension), but this 
physical action now discovered is a quite general one, without 
exceptions. No case was found of the cells of a flowering plant 
