RHYTHMICAL ConTRACTIONS IN MuscLE- 519 
Inhis well-known and thorough work on electro-physiology 
the same author adds the following: 
Strong solutions of Na,SO,, as also very dilute solutions of 
NaOH (in 5 per cent. NaCl solution), act in the same way as 
Na.CO;, but not so strongly. In view of the similarity in the 
effects of those substances upon the heart muscle one is justified in 
speaking of a specific action of sodium salts, mentioned above, in 
consequence of which the contractile substance of striated muscle 
is so altered through the presence of even small amounts of these 
substances that it is stimulated to contraction more easily and by 
weaker stimuli than is ordinarily the case.' 
We also know that Ringer has called attention to the 
importance of calcium and potassium salts for the activity of 
the heart, so that one might be inclined to believe that cer- 
tain salts bring about the activity of the heart directly. In 
this connection Howell considers particularly the calcium 
salts.” 
2. It therefore seemed of interest to me to determine 
whether the power to bring about rhythmical contractions in 
skeletal muscle was not the property of certain ions. My 
experiments consisted in observing the behavior of the gas- 
trocnemius muscles of frogs in a series of solutions. The 
muscle was entirely unweighted and unstretched and freed 
from all bone. This fact is to be observed in repeating the 
experiments. Carefully prepared equimolecular or isosmotic 
solutions were used. The chemicals used were chemically 
pure, and the water was twice distilled in glass. As we 
often deal with only very weak contractions, or, more cor- 
rectly, only with a tremor of individual muscle fibers, the 
contractions could not be registered graphically, but could 
only be observed. 
Biedermann has already pointed out that the rhythmical 
contractions of muscles in the solution used by him are not 
entirely similar to the activity of the heart. 
1W. BIEDERMANN, Electrophysiologie (Jena, 1895), p. 92. 
2W.H. HowE.u, American Journal of Physiology, Vol. IT (1898). 
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