478 STUDIES IN GENERAL PHYSIOLOGY 
cases increase simultaneously with the valency. To say that 
the toxicity increases in proportion to the increase in atomic 
weight would be entirely wrong. The atomic weights are 
9.08 for Be, 24.3 for Mg, 39.9 for Ca, 87.3 for Sr, and 136.9 
for Ba. If the toxicity of the ions were proportional to 
their atomic weights, this would show itself clearly in our 
experiments. The velocities of migration correspond much 
more perfectly with the relative toxicities of these ions. 
According to Kohlrausch, the velocities of the ions at 18° 
are about as follows: 4Mg = 42, 4Ca—49, 4Ba—53. Sr 
is not given, but the velocity of its ion might stand close to 
that of Ba. One sees that this series of velocities does not 
show the jump which occurred in the former series from Na 
to K, and which corresponded to a similar jump in the rela- 
tive toxicities. The difference in the velocity of migration 
of Mg and Ca is only 10 per cent., while that between the 
corresponding members of the Li series, namely, Na and K, 
is 50 per cent. We see also that no such jump exists from 
the toxicity of Mg to that of Ca. The conclusion seems 
justified, therefore, that the relative toxicities of the series 
of ions Be, Mg, Ca, Sr, and Ba correspond more nearly to 
the velocities of these ions than to their atomic weights. 
We have yet to discuss the toxicity of the anions. OH, 
with its enormously high velocity of migration, is, as we have 
seen, a relatively strong poison for muscle. On the other 
hand, the Cl ion, with a speed of migration which is equal 
to that of the K ion, is as harmless as the Li and Na ions, 
as is shown by the behavior of the 0.7 per cent. NaCl solu- 
tion, which contains just as many Cl ions as Na ions. The 
speed of migration of the NO, ion is, according to Kohl- 
rausch, 60 at 18°; that of 480,, 66; that of Cl, 62. The 
fact that $H,SO,, HNO,, and HCl show themselves to be 
equally poisonous at the same concentration indicates that 
in the concentrations which we employed the effect, of the 
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