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 cc. | n NaCl + 10 c.c. distilled water 



80 " " +20 " " 



70 " " +30 " etc. 



The result of the experiments was that the Gonionemus con- 

 tracts longest in a mixture of equal parts of a f 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) 96 c.c. | -n NaCl + 4 c.c. *n MgCl 2 



(2) 96 " " + 4 c.c. | n KC1 



(3) 96 " " +4 c.c. YwCaCl, 



In the first two solutions the Medusae make a few contractions 

 during the first minute, and then stop. In the third solution 

 the rhythmical contractions may go on for an hour. If we 

 take 2 c.c. of the CaCl 3 , KC1, and MgCl 2 solution (instead 

 of 4 c.c.), the results are practically the same. After this 

 the following solutions were tried: 



(1) 96 in NaCl + 2 c.c. ^-n MgCl 2 + 2 c.c. f n KC1 



(2) " '' + " " +2 c.c. J^nCaCla 



(3) " " + " f n KC1 +2c.c.VwCaCl 2 



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 



