554 STUDIES IN GENERAL PHYSIOLOGY 
in the ion proteids, and this restores the irritability (or con- 
tractility) of the Medusa. We thus see again that the Na ions 
in a pure NaCl solution are poisonous. If this idea were 
correct, we should expect that in a more diluted NaCl solu- 
tion the Medusa would be able to contract much longer. 
This is indeed the case. I tried the following solutions: 
90 ec. §n NaCl +10 ce. distilled water 
gs « « +20 « 7 
70“ “+30 “ : ete. 
The result of the experiments was that the Gonionemus con- 
tracts longest in a mixture of equal parts of a §n NaCl solu- 
tion and distilled water. The case is parallel to that of 
Fundulus, with the exception that the Gonionemus is not 
able to stand distilled water. Otherwise the NaCl is the less 
poisonous for Gonionemus the more dilute it is. We are 
forced to conclude that if we add certain other metal ions to 
the NaCl solution, its poisonous effects must disappear. 
We tried the following solutions: 
(1) 9% ce. $n NaCl+4cc.42n MgCl, 
(2) 96 * “ +4ee $n KCl 
(3) 9% “ “ 44e¢.42n CaCl, 
In the first two solutions the Medusz make a few contractions 
during the first minute, and then stop. In the thirdsolution 
the rhythmical contractions may go on for an hour. If we 
take 2 c.c. of the CaCl,, KCl, and MgCl, solution (instead 
of 4 c.c.), the results are practically the same. After this 
the following solutions were tried: 
(1) 26 én NaCl+2 cc. 42n MgCl, +2ec. § n KCl 
(2) ee a “ +2 ce. 42 CaCl, 
(3) eo“ +“ $n KCl 420.407 CaCl, 
In solution 1 no contractions occurred, while in solutions 2 
and 3 regular contractions set in, whose period was almost 
normal. They lasted an hour or more. Mg ions act in this 
case more like K ions. We thus see again that for the 
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