522 STUDIES IN GENERAL PHYSIOLOGY 



the contractions, one would expect that an increase in the 

 osmotic pressure of the active ions should also be able to 

 cause rhythmical contractions to set in more quickly. We, 

 indeed, find that a solution having a greater concentration 

 than that of a 0.7 per cent. NaCl solution brings about con- 

 tractions sooner. In a 1.4 per cent. NaCl solution contrac- 

 tions begin immediately and continue uninterruptedly; in a 

 1.05 per cent. NaCl solution contractions often do not begin 

 until several minutes after the immersion of the muscle in 

 it; in a 0.7 per cent. NaCl solution rhythmical contractions 

 only begin after one or one and a half hours. In the highly 

 concentrated solutions the contractions begin immediately, 

 but they also cease very soon, What has been said here for 

 NaCl solutions holds good also for the solutions of other 

 ions capable of calling forth contractions ; for example, NaBr 

 or LiBr solutions. I had solutions of these two salts which were 

 isosmotic with the following NaCl solutions: 3.5, 2.8, 2.1, 1.4, 

 1.05, and 0.7 per cent. In the latter concentration it often took 

 some time before rhythmical contractions began, while in the 

 solutions of a greater concentration contractions developed 

 immediately. In solutions isosmotic with a 1.4 per cent. 

 NaCl solution maximum contractions set in at once; while 

 in the next weaker solution, 1.05 per cent, maximum con- 

 tractions occurred only after some time. In these strongly 

 concentrated solutions the rhythmical contractions did not, 

 however, continue for so long a time as in the 0.7 per cent. 

 NaCl solution, or in solutions of NaBr or LiBr isosmotic 

 with this. 



5. The fact that in salt solutions of high concentration 

 the contractions soon cease points without doubt to an injury 

 of the muscular substance through the salt solution used. I 

 expected that as soon as the contractions ceased in a salt 

 solution the periodic irritability of the muscle had also 

 fallen below a certain point. But this was, however, by no 



