The Plasmatic Membrane. 
i *3 
be able to accumulate more strongly at the surface than the 
true solutes, as the force redistributing them will be slighter. 
Sugars have only a very slight effect on surface-tension ; salts, 
which raise surface-tension, will be repelled from the surface ; 
while proteids and fatty substances which lower surface-tension, 
will accumulate at the surface and tend to form a more concen¬ 
trated layer. Of these substances, the fatty substances (lipoids), 
including neutral fats, soaps, lecithin, cholesterin, etc., lower 
surface tension very much more than do proteids, and so they 
will be relatively more abundant in the surface layers. 
There is no way of ascertaining the thickness of the super¬ 
ficial strata affected by this surface-concentration, but it is below 
the limit of microscopic visibility, and Ostwald states the special 
surface-properties of a drop of water extend only to depth of about 
one millionth of a millimetre. 
The application of these general principles of surface-action 
and micro-chemistry to the living cell may be postponed till we have 
reviewed the contributions of Czapek and Lepeschkin to our 
knowledge of the plasmatic membrane. 
II.—Czapek’s Researches on the Plasmatic Membrane. 
The four papers by Czapek referred to at the beginning of this 
article make a most interesting series in which we find an 
admirable prosecution of a line of investigation, ending in the 
discovery of a new general attribute of living plant-cells. The first 
paper sets out the details of a study of the precipitates that can be 
produced inside the living cell by certain agents of a basic nature. 
Charles Darwin, in 1876, described the phenomenon of “ aggre¬ 
gation ” in the red cells of the tentacles of Drosera, that was 
produced by dilute ammonia. On application of this agent, fine 
red drops appear in the cells and these run together to bigger 
globules and may ultimately form one large irregular “myelin¬ 
like ” mass in each cell. Loew and Bokorny showed similar 
colourless aggregation in the mesophyll cells of Echeveria, and 
found that caffein (02% solution) is better than ammonia for pro¬ 
ducing them. Czapek has extended their observations and finds that 
practically all plant-cells that contain tannin give this effect and 
that cells containing the tannoid substance anthocyan are the 
easiest for observation, 
The appearance of the precipitate suggests a fatty substance, 
but by careful tests Czapek shows that the bulk of it is a loose 
