EFFrect or Ions upon TISSUE 573 
The problem is the same as forGonionemus. In the latter it 
ss certain that under ordinary circumstances (7. e., in the 
oresence of the K and Ca ions of the sea-water),the impulses 
for the rhythmical contractions originate in the nervous 
system, or at least in the margin. It is, however, not the 
histological or morphological structure of the ganglia which 
allows them to be so important, but their chemical constitution. 
The center of Gonionemus is able to beat rhythmically in a 
pure NaCl or NaBr solution. It is true that the center of 
Gonionemus (and the apex of the heart) contain single scat- 
tered ganglion cells. One might think that these latter are 
responsible for the rhythmical contractions of the center 
which occur in pure NaCl or NaBr solutions. But the mus- 
cles of the skeleton (even if curarized) show rhythmical con- 
tractions in the same pure NaCl or NaBr solutions, provided 
the latter do not contain any K or Ca ions. 
2. It would be unwarranted to say that Ca or any other 
ions are the cause of, or the stimulus for, the rhythmical con- 
tractions in Gonionemus, or the heart, or any other organ. It 
would be much nearer the truth to assume that for the possi- 
bility of rhythmical contractions the Na, Ca, and K ions must 
exist in definite proportions in the tissue which is expected to 
show rhythmical activity. Only so long as these propor- 
tions are preserved does the tissue possess such physical 
properties and such labile equilibrium as to be capable of 
rhythmical processes or contractions. If the tissue has per- 
manently or temporarily more Ca and fewer Na ions than 
are required for the above-mentioned physical properties 
and condition of equilibrium, an increase of Na ions in the 
tissue will cause rhythmical contraction. In such a case the 
tissue will begin to contract rhythmically or beat at an 
increased rate in a pure NaCl solution. If the tissue, how- 
ever, contains too many Na and too few Ca ions, a further 
increase of the latter in the tissue will cause the beginning 
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