476 STUDIES IN GENERAL PHYSIOLOGY 
atomic weights. On the other hand, we notice a beautiful 
agreement between the relative toxicity of the individual 
members of this group and the velocity of the migration of 
the ions. According to Kohlrausch, the speed of migration 
of the Li ion at 18° is 33, that of the Na ion 41, that of the 
K ion 60. The velocities of the ions of Rb and Cs are equal 
to the velocity of K, according to Ostwald. A great jump, 
therefore, occurs from Na to K in the velocity of the migra- 
tion of the ions, while no such jump occurs from K to Rb 
and to Cs, just as is the case in their toxicity. It may 
therefore be said that the relative toxicity for muscle of the 
ions of this group is rather a function of their velocity of 
migration than of their atomic weight. The heavier ele- 
ments are, therefore, more poisonous only because their ions 
have a greater speed of migration than the Na and Li tons. 
On the other hand, the toxicity of K ions is much less 
than that of the hydroxyl ions. In our experiments with 
alkalies the addition of 10 c.c. of a one-tenth normal alkali 
solution to 100 ¢.c. of a physiological NaCl solution was 
sufficient to bring about a decided decrease in irritability. 
It did not matter, however, whether the alkali used was 
KOH, NaOH, or LiOH. At this concentration only the OH 
ions were poisonous, while the toxicity of the K ions did not 
appear. 
The investigation of the relative toxicity of the bivalent 
ions Be, Mg, Ca, Sr, and Ba is rendered difficult by the fact 
that a solution of the chlorides of these elements of the 
same concentration as a 0.7 per cent. NaCl solution has a 
greater osmotic pressure than the sodium-chloride solution. 
The muscle, therefore, loses water (as we have seen) in such 
a solution, and the loss in water must also decrease the irri- 
tability. We are, however, in a position to estimate the 
influence of the loss of water on the irritability. The loss 
of water in these solutions was about equal to that in a 1.05 
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