474 
PHYSIOLOGY: J. LOEB 
efficient for this purpose as NaCl.^ I showed later that the poisonous 
effects of NaBr, NaNOs, and other salts, could also be annihilated 
by the addition of NaCP and the same was found to be true for the 
effect of acids. ^ Since a pure solution of NaCl does not diminish but in- 
creases the permeabiHty of the membrane it was not possible to explain 
these cases on the assumption of an opposite influence of the antagonistic 
electrolytes upon the permeability of the ceil wall. I have recently 
made some experiments in collaboration with Mr. McKeen Cattell 
which have led me to a theory which seems also to furnish the physico- 
chemical analogue to this second group of phenomena of antagonism. 
We found that the same concentration of KCl in distilled water 
causes the standstill of the heart of the embryo much more quickly 
than when contained in sea water. This experiment (which we will 
call experiment I) is simply a confirmation of the previous experiments 
of Loeb and Wasteneys on the adult fish, and it might be interpreted 
on the assumption that the permeability of the membrane for KCl is 
greater in distilled water than in sea water. But this explanation of 
experiment I is rendered impossible by experiment II which follows. 
Eggs were exposed to a KCl solution until the heart stopped beating. 
They were then equally distributed in distilled water and in sea water 
and it was observed in which of the two solutions the hearts began to 
beat first. The result was very striking. While the hearts of the 
eggs in the sea water began to beat again in a few hours, or in less than 
a day, those in distilled water often did not recover in a number of 
days. When their recovery failed to occur within reasonable time in 
distilled water the heart beat could be called forth in less than a day 
by transferring the eggs to sea water. 
The recovery of the hearts poisoned with KCl depends upon the dif- 
fusing out of the KCl from the egg. If it is legitimate to assume in 
experiment I that in distilled water the KCl causes the heart to stop 
more quickly because the membrane is more permeable for KCl in 
distilled water than in sea water, we should expect that in the recovery 
experiment the hearts would also begin to beat sooner in distilled water 
than in sea water; since in the latter the membrane is assumed to be 
less permeable than in distilled water. Hence in sea water it should 
require more time for the excess of KCl to diffuse out of the egg than in 
distilled water, which is the reverse of what we observed. It is, there- 
fore, impossible to explain these observations on the assumption that 
in distilled water the permeability of the cell membrane for KCl is 
greater than in sea water. 
3. We next tried whether other substances acted like sea water, and 
