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OSMOTIC PRESSURE. 7
which do not cause plasmolysis, act in aqueous solution in the same
manner upon the blood corpuscles as pure water. This has been espe-
cially shown by the investigations of Gryns.1
Different investigators have attempted to perform plasmoh tic
experiments with animal cells, but without any special result. With
the microscope one can often observe that the red blood corpuscles
shrink under the influence of a strong salt solution, but the limit solu-
tion when the shrinking just begins cannot be exactly determined because
the changes in volume are so very small. If we summate the changes
in volume of many corpuscles, which can be done by centrifuging the
blood mixture in a graduated tube, then very small changes can be detected.
Such determinations have been made by Hedin,2
Koeppe 3
and others.
It was found that the blood corpuscles swell in a weak salt solution,
shrink in a stronger solution, and there is a certain concentration which
does not change the volume. By determining the freezkig-point Hedin
found that this concentration for NaCl was nearly isosmotic with the
serum of the blood corpuscles used. The depression of the freezing-
point was about 0.56° and the concentration of the NaCl solution is
0.9 per cent, or about 0.15 normal.
The question as to the permeability of the blood corpuscles has been
investigated by Hedin, using a method depending upon the following:4
The depression of the freezing-point of a solution is proportional to its con-
centration. A certain amount of the substance to be tested is dissolved in blood.
The serum of this treated blood freezes at a lower temperature than before the
salt was added. The depression of the freezing-point can be designated as a.
Now the same amount of substance is dissolved in serum using the same volume
of serum as blood was previously used. The depression of the freezing-point
of this serum can be designated as b. From this it is evident that a =6 if
the blood corpuscles take up just as much dissolved substance from the blood
as an equal volume of serum. If the blood corpuscles take up less than the serum
then a> b or-r > 1 , and when they take up more than the serum then a <b or-? < 1.
The result r, in the calculation of which the change taking place in the volume
of the blood corpuscles on the addition of the substance must be considered,
gives immediately an approximate idea of the quantity of substance which has
passed into the blood corpuscles.
The results were as follows:
The salts of the fixed alkalies and alkaline earths, neutral amino-
acids, varieties of sugars as well as hexatomic and pentatomic alcohols
pass into the blood corpuscles only to a slight degree. Erythrite (tetra-
1
Pfluger’s Arch., 63, 86 (1896).
2
Skand. Arch. f. Physiol., 5, 207, 238. 377 (1895).
3
Arch. f. (Anat. u.) Physiol., 1895, 154.
4
Pfluger’s Arch., 68, 229 (1897); 70, 525 (1898).
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