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. Ina 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 
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