THE PuysioLoGicaL Errects oF Ions 475 
muscle in one hour. The hydroxyl ions act much more 
weakly. When 20 c.c. of a one-tenth normal LiOH, NaOH, 
or KOH solution were added to the NaCl solution, the 
irritability was greater or just as great as when 10 c.c. of the 
acid solution were added. The speed of migration of the 
hydrogen ions is, according to Ostwald, 325 at 25°, that of 
the hydroxyl ions 170. 
If we study the monovalent cations Li, Na, K, Rb, and 
Cs, it is to be remembered that at the concentration which I 
employed of 1 mol. in about 8 liters of water the dissocia- 
tion of the chlorides of these elements is so complete (84 per 
cent.) that we are dealing chiefly with the effects of ions. 
Of these ions Li and Na were not poisonous, so far as the 
irritability of the muscle was concerned, for the irritability 
remained unchanged. On the other hand, the ions K, Rb, 
and Cs, with their greater atomic weight and greater velocity 
were decidedly poisonous. The irritability of the muscle in 
the KCI solution (of the same concentration as a 0.7 per 
cent. NaCl solution) was almost destroyed after one hour, or 
at any rate greatly decreased. The same is true of RbCl 
and CsCl solutions of the same concentration as a 0.7 per 
cent. NaCl solution. 
It cannot be concluded from my observations that the 
toxicity of the Rb and Cs ions is greater than that of the K 
ions. I am rather inclined to believe that the toxicity of the 
three last-named ions for the gastrocnemius of the frog is 
about the same. I thought at first that the toxicity of the 
ions was a function of their ionic weight. Such a view is, 
however, untenable when the atomic weights are considered. 
The atomic weight of Li is 7, that of Na 23, that of K 39, 
that of Rb 85.2, that of Cs 132.7; and yet there is a great 
jump from the toxicity of the sodium ions to that of the 
potassium ions. The latter are, however, about as poisonous 
as Rb and Cs ions, in spite of the great differences in their 
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