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OSMOTIC PRESSURE. 9
in connection with other tissue constituents. By investigations on the
changes in the weight (instead of the volume changes in the above-mentioned
experiments with plant cells and blood corpuscles) which frog muscles
undergo in solutions, various experimenters, Nasse, 1
Loeb,2
and Over-
ton,3
have tried to prove the ability of muscle to take up various substances.
Overton found that as long as the irritability of the muscle was retained
the muscle took up the same bodies as the plant cells. The sarcolemma
is not responsible for the permeability, but the outer layers of the muscle
protoplasm are.
The skin of amphibians seems according to Overton to behave like the muscles 4
in regard to permeability.
Theories of Admissibility. On what does the permeability or non-
permeability of membranes and of cells for certain bodies depend? The
discoverer of precipitation membranes, M. Traube, considered the mem-
brane as a sort of molecular sieve. The relation of the size of the particles
passing and the width of the pores of the membrane is important.5
This
view cannot be contested. The copper ferrocyanide membrane may be
considered to act in this way and the non-permeability of most mem-
branes for colloid substances depends upon the fact that the pores are
too narrow for the particles.
The question as to the occurrence of a special outer limiting layer
of the cells is of interest for the understanding of the metabolism of the
cells as well as for the knowledge as to the manner in which the cells take
up and give out substances. In this connection it must be recalled that
in the protoplasm of certain cells we find an outer dense layer or a true
membrane which seems to consist of protein substances. Still, even in cells
in which no special outer limiting layer can be seen, the presence of such a
limiting layer must be admitted because of the permeability condi-
tions of these cells.
Nernst 6
has shown, by special experiments, that the permeability
of a membrane for a certain substance is essentially dependent upon
the solvent power of the membrane for this substance. This question
which is very important for the study of the osmotic phenomenon in
living cells has been especially studied by Overton.7
From the behavior
1
Pfluger’s Arch., 2, 114 (1869).
i
Ibid., 69, 1; 71, 457 (1898).
J
Ibid., 92, 115 (1902); 105, 176 (1904).
* Verhandl. d. phys. med. Gesellsch. zu Wurzburg (N. F.), 36, 277 (1904).
5
Arch. f. Anat. Physiol, u. Med., 1867, 87.
6
Zeitschr. f. physikal. Chem., 6, 37 (1890).
7
Vierteljahrsschr. d. Naturf. Gesellsch. in Zurich, 44 (1899) and Overton, Studien
uber die Narkose, Jena, 1901.
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