RHYTHMICAL CONTRACTIONS IN MUSCLE 529 
To these belong first of all the K ions. I prepared a series 
of potassium compounds, all of which were isosmotic, with a 
0.7 per cent. NaCl solution, namely, KCl, KBr, KI, K,S0O,, 
and potassium oxalate. Rhythmical contractions did not 
occur in any of these solutions. We know, however, that 
Br ions have the power of causing rhythmical contractions, 
or at least are able to accelerate the appearance of these con- 
tractions, for in NaBr the contractions occur much sooner 
than in an isosmotic NaCl solution. Potassium must, there- 
fore, prevent the contractions. 
The sodium compounds corresponding to the potassium 
compounds just given are all able to bring about rhythmical 
contractions. 
Ca also inhibits the contractions; and not only this, but 
the entire group, Be, Mg, Ba,’ Sr, and also Mn and Co. No 
contractions occur in these solutions. 
The behavior of Ca is so characteristic and its réle in the 
phenomena of contractions of such significance that I shall 
have to discuss this point in greater detail. 
In one series of experiments I used the following solutions: 
a) 100 c.c. NaBr isosmotic with a 0.7 per cent. NaCl 
solution. 
b) The same plus 2 ¢.c. of an equimolecular CaCl, solu- 
tion (about 1.33 per cent.). 
c) The same with 3 c.c. of the CaCl, solution. 
d), e), f) The same with 4, 5, and 6 c.c. respectively of 
the CaCl, solution. 
The percentage of CaCl contained in the various solutions 
was, therefore, in order as follows: 0.0265, 0.0387, 0.0511, 
0.0633, 0.0744 per cent. A fresh gastrocnemius muscle 
was introduced into each of these solutions. The concen- 
tration of the CaCl, in the second solution was equal to 
1Tt was found later on that Ba salts cause contractions in a low concentration. 
This had been noticed before. Why this was at first overlooked by me I cannot tell. 
[1903] 
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