564 STUDIES IN GENERAL PHYSIOLOGY 
Gonionemus. If a Gonionemus is thrown into a solution of 
98 cc. Sn NaCl+2 cc. 19 CaCl, solution or a pure in 
NaCl solution, it stops contracting after a certain time, but 
beats again for a little if thrown into a solution with more 
CaCl, (for instance, 95¢.c. §n NaCl + 5c¢.c.12nCaCl,). This 
seems to favor the assumption that the Ca ions are the stimulus 
for the contraction of the swimming-bell of a Medusa. But 
a simple control experiment shows that this assumption is 
erroneous. If we throw a Gonionemus first into the stronger 
solution (for instance of 95 c.c. $n NaCl +5 c.c. $n CaCl,), 
and wait until it stops contracting, it will begin to contract 
again if we put it back either into the solution with less 
CaCl, (for instance, 98 c.c. $n NaCl+2 cc. 42 CaCl,) 
or into a pure NaCl solution. The true explanation of this 
phenomenon is, I believe, as follows: In the pure NaCl 
solution or the solution with little CaCl,, too many Na ions 
combine with the proteids, and this leads to a loss of irrita- 
bility. If the Gonionemus be brought into a solution 
with more Ca and less Na ions, some Ca ions will take the 
place of Na ions in the tissues, and this restores the irrita- 
bility. But finally too many Ca ions enter, and the physical 
qualities are changed again, thus making the Gonionemus 
inirritable. If the same Gonionemus then be put into a 
pure NaCl solution or into a NaCl solution with fewer Ca 
ions, the Na ions will take the place of some of the Ca ions, 
and this will restore the irritability. 
We thus arrive at the conclusion that the rhythmical 
contractions of Gonionemus depend upon the presence of 
Na, Ca, and K ions in definite proportions in the ion pro- 
teids of the tissues. These proportions evidently differ in 
various kinds of tissues. Myogenic contractions are pre- 
vented by a smaller amount of K and Ca ions in the sur- 
rounding NaCl solutions than neurogenic contractions or 
contractions originating in parts containing ganglia. 
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