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, KC1, KBr, KI, K 3 SO 4 , 

 and potassium oxalate. Rhythmical contractions did not 

 occur in any of these solutions. We know, however, that 

 Br ions have tlie 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, 1 Sr, and also Mn and Co. No 

 contractions occur in these solutions. 



The behavior of Ca is so characteristic and its role 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. 



6) The same plus 2 c.c. of an equimolecular CaCl 2 solu- 

 tion (about 1.33 per cent.). 



c) The same with 3 c.c. of the CaCl 2 solution. 



d), e),f] The same with 4, 5, and 6 c.c. respectively of 

 the CaCl 2 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 2 in the second solution was equal to 



'It 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] 



