The Plasmatic Membrane. 
187 
Fat and soluble in water, like the salts and sugars which form the 
basis of metabolism, would be easily understandable, whereas on 
the older view there was a complete impasse in this direction. 
Present developments of these views give no clue to why some 
water-soluble substances are taken up by the cell and others not. 
In his pamphlet Czapek gives a long list of parts of flowering 
plants which serve to demonstrate this genera relation of surface- 
tension and exosmosis ; and among them there are no exceptions 
to the 0.68 rule. 
Yeast, however, requires a lower surface-tension down to 0’5 
or 0 f 6 to bring about exosmosis of its invertase, and here it may be 
that lecithin or cholesterin is the lipoid in its surface-layer, as 
these two have just such a very low surface-tension in solution. 
Whereas 10% ethyl alcohol causes exosmosis in higher plants, 15% 
is needed for yeast, and the same is true for the exosmosis of 
haemoglobin in haemolysis of red blood-corpuscles. 
Czapek also discusses in some detail the action of narcotics on 
which Overton based his lipoid theory, but that matter cannot Jbe 
gone into here. It must be pointed out that Overton finally 
assumed the activity of lecithin and cholesterin in the normal 
plasmatic membrane, but the new evidence seems to favour the 
presence, not of these particular lipoids, but of neutral fats, except 
in the case of yeast, and no doubt some other lower organisms. 
III.—Lepeschkin’s Researches on the Plasmatic Membrane. 
Concurrently with the publication of Czapek’s four papers 
there appeared four papers by Lepeschkin approaching the same 
subject from quite a different point of view. 
In 1906 Lepeschkin began researches upon the permeability of 
protoplasm, being led to these by his excellent study of the 
mechanism of water-secretion in Pilobohts. A number of papers 
which followed this work dealt with alterations of the degree of 
permeability of protoplasts as a factor in modifying cell-turgor and 
the production of movements in Mimosa and in nyctitropic plants. 
To these were added papers on turgor and permeability in 
relation to growth, and finally in 1910 and 1911 the four papers now 
to be considered, dealing directly with the constitution and organi¬ 
sation of the plasmatic membrane, 
We may take first the new experimental work that is contained 
in these papers and postpone till afterwards the theoretical views 
and detailed discussion of the physical organisation of the plasma- 
