na of osmosis are naturally of the
first importance in the action of organisms, and for a long time have
attracted the attention of naturalists. 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. If, however, the experimental difficulty has not
been overcome in an entirely satisfactory manner, it at least appears
very probable that such walls may nevertheless exist.[16]

[Footnote 15: See next note.--ED.]

[Footnote 16: M. Stephane Leduc, Professor of Biology of Nantes, has
made many experiments in this connection, and the artificial cells
exhibited by him to the Association francaise pour l'avancement des
Sciences, at their meeting at Grenoble in 1904 and reproduced in their
"Actes," are particularly noteworthy.--ED.]

Nevertheless, in the case of gases, there exists an excellent example
of a semi-permeable wall, and a partition of platinum brought to a
higher than red heat is, as shown by M. Villard in some ingenious
experiments, completely impermeable to air, and very permeable, on the
contrary, to hydrogen. It can also be experimentally demonstrated that
on taking two recipients separated by such a partition, and both
containing nitrogen mixed with varying proportions of hydrogen, the
last-named gas will pass through the partition in such a way that the
concentration--that is to say, the