124. REPORTS ON THE STATE OF SCIENCE.—1918. 
up into several smaller pieces, these parts when free assume a spher- 
ical shape, and form at once on their surfaces a layer with the 
same properties as regards permeability as the original protoplasmic 
membrane had. 
If the cell substance is in contact with a liquid containing various 
substances in solution, as in the tissues of the higher plants and 
animals and in the case of the vacuoles in the interior of the cell, 
then the surface film will contain constituents of both phases and its 
properties will not be identical with those of a membrane formed in 
contact with water only. Evidence of this was fourd by Osterhout 
(1913). ; 
It is obvious that the properties of the cell membrane as regards 
permeability to solutes both in the external liquid and in the interior 
of the protoplasm must play an important part in the life of the cell. 
While it is impossible to deny thata film of some sort must be formed, 
it is held by some investigators that sufficient evidence does not exist 
that it is possessed of the property of semi-permeability, at all events 
as regards crystalloids (see especially Moore and Roaf, 1908). If this 
be so, it is clear that the escape of such constituents from the cell 
must be prevented by their existence therein in fixed combination 
with solid parts. The evidence on this question must be examined. 
There is no doubt that the salts present inside a cell may differ, 
not only in concentration, but in their chemical nature, from those in 
the external liquid. Perhaps the most striking case is that of the red 
blood corpuscles of the rabbit. Abderhalden (189%, p. 100) found 
that the blood serum contains 0:44 per cent. vf sodium salts, while 
the corpuscles contain none at all; whereas the corpuscles contain 
twenty times as much potassium salts as the serum does. Similar 
facts have been described in the case of the muscle cells. The 
behaviour towards acid and alkali is interesting. Neither hydro- . 
chloric acid nor sodium hydroxide is capable of entrance into the 
uninjured cell. If jellyfish are allowed to swim in sea water to 
which neutral red has been added, they take up the dye into their 
cells, where it has the orange-red colour of the neutral solution. 
Bethe (1909) added hydrochloric acid until the colour of the dye in 
the water was changed to the cherry red of the acid solution. But 
the contents of the cells underwent no change in colour until enough 
acid had been added to stop the movements and kill the organisms. 
Warburg (1910) showed that the colour of neutral red inside the eggs 
of the sea urchin, which are acid, was unchanged by the addition of 
sodium hydroxide to the water, but immediately , changed tu yellow 
by a small quantity of ammonia. 
But, it may be said, no evidence has been given that the electro- 
lytes inside the cell are free to diffuse, even if the membrane allowed 
them to pass. The fact that the osmotic pressure inside cells is too 
great to be accounted for except by the presence of small molecules 
in the free state is indirect proof. Animal cells require, to prevent 
their swelling and rupture by osmosis, an external solution equivalent 
to 5:4 per cent. glucose or 0°9 per cent. sodium chloride ; that is, a 
solution of 0°3 molar concentration. The osmotic pressure of this is 
6°7 atmospheres. If we take a colloid which has as great an osmotic 
pressure as hemoglobin has, we find, on calculation, that a solution 
v.97 =o8 i 
