528 STUDIES IN GENERAL PHYSIOLOGY 
of an alkali. If 2 or 3 ¢.c. of a4, normal LiOH solution is 
added to 100 ¢.c. of a KCl solution isosmotic with a 0.7 per 
cent. NaCl solution, no rhythmical contractions occur. 
One might think that acids and alkalies increase the 
irritability, and that for this reason their addition would 
accelerate the contractions. We find, however, that in cer- 
tain solutions periodical contractions occur when the irrita- 
bility has been decreased, while in other solutions these 
contractions do not occur at all even when the irritability is 
normal or above normal. In 100 c.c. KCl solution to which 
had been added 2 c¢.c. of a =; normal LiOH solution the 
muscle was still irritable after half an hour when the 
secondary coil was 420 mm. away from the primary, without 
a single contraction occurring, while another muscle the irri- 
tability of which had dropped to 8300 mm. in a LiCl solution 
still gave strong rhythmical beats at the same time. It can 
further be easily shown that the addition of an acid which 
accelerates the beginning of contractions soon decreases 
markedly the irritability of the muscle. 
I am much more inclined to go back to the first explana- 
tion given, that certain ions—for example, Na ions—bring 
about rhythmical contractions in that they enter the muscle 
and here form definite compounds. H and OH ions have a 
catalytic action; that is, they accelerate the formation of 
these compounds. It might also be that they owe their 
activity to their power of splitting off the material necessary 
for the formation of the compounds with the Na ions.' 
10. We have thus far become acquainted, first, with a 
group of ions which are able to bring about rhythmical con- 
tractions in skeletal muscle (Li, Na, Rb, Cs, F, Cl, Br, I); 
secondly, we have seen that H and OH ions accelerate the 
appearance of the effect of the ions just named. There isa 
third class of ions which inhibit rhythmical contractions. 
1Jt is also possible that through their effect on the lipoids they increase the 
permeability of the muscle for Na and other ions or salts. [1903] 
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