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The Plasmatic Membrane. 
Granted that a protoplast is a close approximation to a true 
fluid, what can we say about the thickness of the surface-layer, that 
is the layer in which there is a special accumulation of active 
substances? Will it be thin and invisible as in a perfect fluid, or 
does it correspond with the “ Plasmahaut” for which many observers 
have noted a difference of appearance and which Lepeschkin 
finds to be less stable than the rest of the protoplast ? 
The Lipoids of the plasmatic membrane and selective permeability. 
With unusual agreement, all lines of investigation point to the 
presence of lipoids in the plasmatic membrane. What may be the 
significance of this occurrence ? These substances are held by 
Overton and others to condition the selective permeability of the 
cell for organic substances, but the selectivity shown is from a 
chemical point of view quite arbitrary and, biologically, probably of 
no significance, though oxygen and carbon dioxide are more soluble 
in fats than in water. No one has yet risen to affirm that we 
should regard as a biological adaptation the fact that all living cells 
when brought into contact with fat-solvents pass into the curious 
state which we call narcosis, although in these days of anesthetic 
surgery, this property has become of infinite advantage to the 
individual. 
Is it possible then that this distribution of lipoids in the cell is 
merely a necessary incident of the action of the Gibbs-Thomson 
rule upon the fats present in the cell for metabolic purposes ? 
The rule itself, with its thermo-dynamic basis, cannot be 
abrogated and the only obscurity is as to whether in so complex an 
organisation as that of protoplasm the emulsion particles of lipoids 
would be free and mobile enough to respond by the expected 
surface-accumulation. 
It is satisfactory to find that both investigators have thrown 
off the incubus of Overton’s theory of a continuous film of lipoid 
matter on the surface of the protoplast. While Lepeschkin inclines 
to the view that the lipoid present is lecithin combined with the 
proteid, Czapek’s evidence favours the view of a saturated emulsion 
of neutral fat. It is true that a surface-tension of 0-68 could be 
obtained with the right amount of lecithin, short of saturation, but 
the wide uniformity of value found for so many plants makes it 
easier to believe in fat which has this as a limiting value and there¬ 
fore small differences of concentration would be unimportant, than 
to believe that exactly the right amount of lecithin is always present. 
If the lipoid layer that Czapek deals with is of ultra-microscopic 
