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6 GENEKAL AND PHYSICO-CHEMICAL.
weaker solutions are called hypotonic, and stronger hypertonic. De
Vries, with the aid of equal cells (cells of the epidermis of the lower
side of the leaf of the Tradescantia discolor) has, for various substances,
determined the concentration of this limit solution. It was found that
the limit solution of analogously constructed salts had the same molec-
ular concentration. Thus the alkali salts of the type NaCl (haloid
salts, nitrate, acetate) plasm olyzed at one molecular concentration and
the salts of the type Na2SC>4 (sulphate, oxalate, diphosphate, tartrate)
at another concentration. If the plasmolyzing power of a molecule
of the first group is equal to 3, then the molecule of the second group
equals 4. The concentration of the limit solution varied in de Vries’
experiments between the limits corresponding to a NaCl solution of
0.6-1.3 per cent.
As above mentioned, only those substances bring about plasmolysis
which cannot themselves pass through the protoplasm envelope of the
cell content, and these substances only in the case that the concentration
is sufficient. If a body is taken up by the protoplasm it produces no
plasmolysis, because its tendency to attract water has been satisfied
by its own passage into the cell. These substances do not produce
plasmolysis in any concentration. If a body slowly passes in, then
at first it causes plasmolysis, but this then ceases later. The plasmolytic
methods have been used by de Vries, and especially by Overton.1
Experiments with Blood Corpuscles. Over a hundred years ago
Hewson observed that the blood corpuscles were destroyed in water,
and that salts in certain concentrations prevented destruction.2
Ham-
burger 3 has carefully and systematically investigated the action of
salts of the alkalies and alkaline earths, and concludes that when blood
is mixed with certain volumes of solutions of different concentrations
of the same salt, all solutions whose concentration lie below a certain
limit cause the exudation of haemoglobin. On comparing the molec-
ular concentration of the limit solution of different salts it was found
that they bore the same relation to each other as the relative figures
found by de Vries for the molecular concentration of the plasmolytic
salt solutions. From this it probably follows that the protective action
of the salts upon the blood corpuscles depends upon the same reason
as the plasmolysis. This conclusion is also supported by the fact that
those substances which, according to de Vries, in proper concentration
cause plasmolysis in living plant cells, can also under similar conditions
prevent the exudation of haemoglobin. Those bodies, on the contrary,
"
Vierteljahwchr. d. Naturf. Gesellsch. zu Zurich, 40, 1 (1895); 41, 383 (1896).
’Phil. Trans., 1773, p. 303.
1
Arch. f. (Anat. u.) Physiol., 1888, p. 31; Zeitschr. f. Biol., 26, 414, (1889).
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