RHYTHMICAL CONTRACTIONS IN MUSCLE 531 



liberation of rhythmical contractions through Na and Br 

 ions. Because of the importance of this fact, I will briefly 

 report another experiment. I repeated the same experiment 

 given above, with this difference, that a 0.7 per cent. NaCl 

 solution was used instead of NaBr. In this case the periodic 

 contractions began in the pure NaCl solution in eighty 

 minutes; in the remaining solutions, which contained a trace 

 of CaCl 2 , contractions did not occur at aliquot even in the 

 solution which contained 0.026 per cent. CaCl 2 . 



It could be shown in these experiments also that the 

 faradic threshold of stimulation of the muscle contained in 

 the solution containing Ca was no lower than that of the 

 muscle which beat rhythmically in the NaCl solution free 

 from Ca. 



In a more concentrated CaCl 2 solution for example, in 

 a solution isosmotic with a 0.7 per cent. NaCl solution not 

 only do no contractions occur, but the faradic irritability is also 

 rapidly destroyed. If, however, only a small amount of Ca 

 is present in the NaCl solution for example, as much as 

 there is contained in an equal volume of serum only the 

 specific inhibiting effect of the Ca ions upon the liberation 

 of the rhythmical contractions through Na and other ions 

 appears, while the irritability does not suffer. 



We therefore come to this necessary conclusion* that there 

 are ions the entrance of which into the muscle has a specific 

 inhibiting effect upon the liberation of rhythmic contractions. 

 For practical purposes the most important of these ions are 

 Ca and K 



11. An apparent contradiction to what has been said 18 

 found when the following experiments are made. Two 

 solutions are prepared, one a 0.7 per cent. NaCl solution, 

 and a second similar solution to which 2 c.c. of an equimo- 

 lecular CaCl 2 solution have been added to 100 c.c. of NaCl. 

 The latter solution then contains the amount of CaCl 2 found 



