474 STUDIES IN GENERAL PHYSIOLOGY 
It is well known that weak solutions of Na,CO, increase 
the irritability of the muscle. NaOH in dilute solution acts 
in the same way. Strange to say, these effects are generally 
attributed to the Na. We are dealing in both cases, how- 
ever, with effects which are brought about solely through 
the hydroxyl ions (see sec. iii) and which have nothing to 
do with the Na ions or the Na compounds. So far as I 
know, this error goes through the whole literature.of physi- 
ology and pharmacology. The chapter of chemical stimula- 
tion as well as the chapter on pharmacology stand in need of 
a thorough revision on the basis of the theory of dissociation. 
VIII. THE VELOCITY OF MIGRATION AND THE RELATIVE 
TOXICITY OF DIFFERENT IONS FOR THE MUSCLE 
It seems to me to be of the greatest interest to compare 
the relative toxicities of ions in order to discover if any rela- 
tions exist between these toxicities and the other properties 
of the ions. 
If I make such a comparison of the toxicity of the ions 
dealt with in this paper, I do it with two reservations: first, 
that although the method of determining the toxicity of ions 
for muscle by determining the threshold of stimulation is 
superior to the method of Kahlenberg, it is, nevertheless, not as 
accurate as that of determining the velocity of migration of 
the ions; secondly, that the observations made thus far refer 
to only a very limited number of ions. I hope to overcome 
the latter shortcoming by further experiments. But I do . 
not yet see how the former difficulty is to be overcome. 
The most poisonous ion (of the ions which have been dis- 
cussed in this paper) for muscle is undoubtedly the hydrogen 
ion, which has the lowest atomic weight, but the greatest 
velocity of migration. For the strength of current and the 
induction apparatus employed by us, 10-15 c.c. of a one-tenth 
normal HCl, HNO, or $H,SO, solution (in 0.7 per cent. 
NaCl solution) sufficed to do away with the irritability of the 
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