PHYSIOLOGY: W. O. FENN 
539 
SIMILARITY IN THE BEHAVIOR OF PROTOPLASM AND 
GELATINE 
W. O. Fenn 
LABORATORY OF PLANT PHYSIOLOGY. HARVARD UNIVERSITY 
Received by the Academy, July 28, 1916 
In the course of experiments on salt antagonism in gelatin, it 
occurred to the writer that it would be possible to find an analogy in 
gelatine for the processes which occur in protoplasm when it is acted 
upon by antagonistic salts. These processes may be illustrated by 
figure 1, which shows changes in the electrical resistance of living 
protoplasm produced by NaCl and CaCl2. If these changes are due 
to the diffusion of salts into the protoplasm (and the resulting increase 
of their concentration) it is possible that similar changes would occur 
in gelatine if it were divided up into small portions corresponding in 
size to the masses of protoplasm which form the individual living cells. 
The increase in the concentration of the salts as they diffused into the 
gelatin would produce changes in the precipitability (and other prop- 
erties) of the gelatine. The manner in which the precipitability varies 
with the concentration of salts has been explained in the previous 
article.^ 
The experiments already reported^ indicate that the favorable 
action of a physiologically balanced solution is due to the fact that 
such a solution produces a precipitate- (or some condition accompany- 
ing precipitation) in the protoplasm, the maximum precipitate being 
found at the isoelectric point. By varying the amount of this pre- 
cipitate, variations in electrical resistance might be brought about. 
If, however, the normal condition of protoplasm is isoelectric, the 
addition of any electrolyte would change this balance and decrease the 
precipitate, thus increasing permeability. It is well known, however, 
from Osterhout's experiments on the electrical resistance of Laminaria,^ 
that salts like CaClo cause a decrease of permeability at first, but this 
is later followed by an increase, while NaCl causes only an increase. 
To make the analogy between gelatine and protoplasm more complete, 
therefore, we should assume that the normal condition of protoplasm 
is somewhat on the anion side of the isoelectric point, i.e., protoplasm 
must bear a negative charge. The addition of CaCl2 would neutralize 
this charge, increase the amount of precipitate or aggregation in the 
protoplasm and thereby decrease the permeability. In excess of Ca, 
however, the precipitate disappears and the permeability increases. 
