THE PHYSIOLOGICAL Errercts or Ions 477 
per cent. NaCl solution. While the irritability of the 
muscle was decreased but little after remaining one hour in 
such a sodium-chloride solution—it fell in one hour from 
420 to 380—it had decreased in a BeCl, solution, for ex- 
ample, to 220 in one hour. In the remaining solutions 
MgCl,, CaCl,, SrCl,, and BaCl, the decrease in irritability 
was still greater. In one experiment, for example, the 
muscle just responded, after remaining for one hour in a 
MgCl, solution, when the secondary coil was pushed out 
110 mm., while the muscle in the CaCl, solution could just 
be stimulated when the coil was at 0. The muscles which 
had been in SrCl, and BaCl, did not respond at all to 
stimuli after an hour. In another experiment a contraction 
could be obtained in a muscle which had been for one hour 
in the MgCl, solution when the secondary coil was at 100; 
for the muscle which had been in CaCl, when the secondary 
coil was at 150; for the SrCl, solution when the secondary 
coil was at 50 to 60; while the muscle which had been for 
one hour in BaCl, was absolutely unirritable. These 
figures show at the same time that this method of determin- 
ing the irritability leaves much to be desired. The follow- 
ing conclusion can, however, certainly be drawn from these 
experiments: The Be ions are decidedly more poisonous 
than the Li ions, even though their atomic weights are 
almost the same; in the same way Mg ions are decidedly 
more poisonous than Na ions, although their atomic weights 
are nearly the same. This fact must also be considered, 
that the dissociation of the chlorides of these bivalent ele- 
ments is less than that of the chlorides of the Li group, and 
that, in consequence, the number of the cations in the Be 
group is smaller than in the Li group. Furthermore, since 
the SrCl, and BaCl, solutions are at least just as poisonous 
as the equally concentrated RbCl and CsCl solutions, it is 
perhaps right to ask whether the toxicity does not in these 
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