THE PHYSIOLOGICAL EFFECTS OF 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 3 solution, for ex- 

 ample, to 220 in one hour. In the remaining solutions 

 MgCl 2 , CaCl 2 , SrCl 3 , and BaCl 2 the decrease in irritability 

 was still greater. In one experiment, for example, the 

 muscle just responded, after remaining for one hour in a 

 MgCl 2 solution, when the secondary coil was pushed out 

 110 mm., while the muscle in the CaCl 2 solution could just 

 be stimulated when the coil was at 0. The muscles which 

 had been in SrCl 2 and BaCl 3 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 2 solution w T hen the secondary coil was at 100; 

 for the muscle which had been in CaCl 2 when the secondary 

 coil was at 150; for the SrCl 2 solution when the secondary 

 coil was at 50 to 60; while the muscle which had been for 

 one hour in BaCl 2 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 3 and BaCl 2 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 



