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10 GENERAL AND PHYSICO-CHEMICAL.
of living cells to dye-stuffs, as well as the special ease in which certain
substances, which are not soluble in water or only slightly so, but are readily
soluble in fats or fat-like bodies, pass into animal and plant protoplasms
has led Overton to the conclusion that the protoplasmic limiting layer
behaves like a substance layer having the solvent properties similar to the
fatty oils. According to Overton the protoplasmic layer is probably
impregnated with lipoids, i.e., bodies more or less similar to the fats
in regard to their solubilities and their solvent power upon certain sub-
stances. The lipoids do not form a chemically definable class of bodies.
Certain of them are still of an unknown constitution while others are
known, especially the lecithins (the phosphatides as a group) and the
cholesterin are to be especially mentioned on account of their great
importance.
The assumption that an accumulation of lipoids occurs, as a special
limiting layer, in the cells is not sufficiently founded and not generally
true at least for the animal cells. Still this assumption is not absolutely
necessary for a comprehension of the action of lipoids in the above
sense. Objections have been raised by a few investigators against
Overton’s theory, which has found general acceptance.1
Thus it fails
to explain all cases, although this was suggested by Overton himself,
for instance according to Cohnheim, it does not explain the absorption
processes in the intestinal canal, and according to Moore and Roaf it
cannot explain certain properties of the cells, namely the varied composi-
tion of the electrolytes within and outside of the cells, and the selective
taking up of certain soluble substances such as food products, drugs,
toxins and antitoxins by the cells. The investigations of the last men-
tioned experimenters are based essentially upon investigations of the
behavior of mineral substances, and they show that the above theory
offers certain difficulties in explaining the exceedingly important exchange
of mineral substances between the cells and the external fluid. Also the
fact that the cells are readily permeable for water is explained with diffi-
culty by Overton’s theory.
J. Traube 2 especially has put forth objections to Overton’s theory.
According to him, the passage of a substance from a watery solution
into the cells, is in the first place due to its so-called solution tenacity in the
watery solution. This solution tenacity is according to Traube the attrac-
tion bf’tween the solvent and the solute; and is not identical with the
osmotic pressure, but is measured by the surface tension of the solution.
1
See O. Cohnheim, Die Physiologie der Verdauunp; u. Ernahrung (1908). J. Loeb
in Oppenheimer’8 Handbuch der. Biochem. Bd. 2, 105. T. B. Robertson Journ. of
biol. Chem., I L908). B. Moore and H. Roaf, Biochem. Journ., 3 (1908).
M’fluger’s Arehiv., 105, 541 (1904); 123, 419 (1908); 132, 511 (1910); 140, 109
(1911).
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