De Vries imagined that the
contractions noticed in the protoplasm of cells placed in saline
solutions were due to a phenomenon of osmosis, and, upon examining
more closely certain peculiarities of cell life, various scholars have
demonstrated that living cells are enclosed in membranes permeable to
certain substances and entirely impermeable to others. It was
interesting to try to reproduce artificially semi-permeable walls
analogous to those thus met with in nature;[15] and Traube and Pfeffer
seem to have succeeded in one particular case. Traube has pointed out
that the very delicate membrane of ferrocyanide of potassium which is
obtained with some difficulty by exposing it to the reaction of
sulphate of copper, is permeable to water, but will not permit the
passage of the majority of salts. Pfeffer, by producing these walls in
the interstices of a porous porcelain, has succeeded in giving them
sufficient rigidity to allow measurements to be made. It must be
allowed that, unfortunately, no physicist or chemist has been as lucky
as these two botanists; and the attempts to reproduce semi-permeable
walls completely answering to the definition, have never given but
mediocre results.
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