1917] BROOKS—PERMEABILITY 315 
protoplasm is at all permeable to lanthanum salts cannot be decided 
with the data furnished by these experiments. 
It might be supposed that the protoplasm was normally more 
permeable to sodium chloride than to the other salts of sea water, 
and that therefore when bathed by pure sodium chloride solution 
more salt would pass through the diaphragm. On the assump- 
tion that the tissue is permeable only to the sodium and potassium 
chlorides, the molecules of which constitute 88 per cent of the 
molecules of salt in sea water, the rise in permeability on substitu- 
tion of sodium chloride solutions for sea water would be only that 
from 88 to 100. The observed rise is much greater, namely, from 
76 to 100, and in addition it must be remembered that the calcium 
and magnesium salts of sea water are probably able to penetrate 
the tissue to some extent. Sodium chloride must increase the 
permeability of the tissue therefore. 
By analogy, it might be assumed that the permeability of the 
protoplasm decreased under the influence of calcium and lanthanum 
salts. In order to obtain more exact information in respect to this 
question, a set of experiments was conducted in which the per- 
meability was determined during successive periods of treatment 
with a given salt. The solutions in both the upper and lower cells 
were renewed at the beginning of each period. The results are 
shown in table IV and fig. 2. 
From these experiments it will be seen that the increase of 
permeability due to sodium chloride is progressive, and that it 
leads in the course of about 4 hours to a permeability of the tissues 
corresponding to that of dead material. The effect of calcium 
chloride, on the other hand, is to cause a temporary decrease in 
permeability, followed by a rise which at the end of about 12 hours 
leads to a permeability comparable with that for dead material. 
At the end of this time the material had assumed the green color 
characteristic of dead material. 
The experiment with sea water was conducted under conditions 
extremely unfavorable to the maintenance of normal permeability, 
the temperature rising to 14° C. during the third and fourth periods. 
Partial recovery is shown in the succeeding periods during which 
the temperature decreased. The last period was begun about 24 
