MUSCULAE TWITCHINGS 755 



or even in 6, which last sometimes as long as fifteen minutes. 

 These contractions are not as rapid as those observed in a 

 pure NaCl solution, and resemble more the normal contrac- 

 tions of a Medusa in sea-water. A series of experiments 

 was undertaken to find out the minimal amount of Ca re- 

 quired to prevent completely all contractions in a pure NaCl 

 solution. In a mixture of 100 c.c. of a f NaCl solution 

 -f- 3 c.c. of a \m Ca(NO 3 ) 2 solution no contractions occurred. 

 A series of experiments with a slightly greater amount of 

 CaCl 2 were made with the same result. 



The same inhibitory effect can be produced if, instead 

 of Ca, Sr or Mg is used. But Ba behaves altogether differ- 

 ently. The following solutions were tested: 



100 c.c. f NaNo 3 



100 c.c. f NaNo 3 + 1 c.c. m BaCl 2 

 100 c.c. NaNo 3 + 2 c.c. m BaCl 2 

 100 c.c. f NaNo 3 + 4 c.c. m BaCl 2 

 100 c.c. f NaNo 3 + 8 c.c. m BaCl 2 

 100 c.c. f NaNo 3 -f 16 c.c. m BaCl 2 



When the center of a Medusa was thrown into any of 

 these solutions, the rhythmical contractions began at once. 

 The center behaved as if the Ba ion had not been present, 

 with this difference, however, that the solutions with a 

 larger amount of barium were more poisonous than a pure 

 NaCl solution. Ba has, therefore, little or no inhibitory 

 effect upon the center of a Medusa. 1 



The analogy between the effect of ions upon muscle and 

 the center of a Medusa goes still farther. I pointed out 

 that possibly the Ca ions in the sea-water and the tissues of 

 the Medusa prevent the isolated center from beating in sea- 



i Since this was written I have received, through the kindness of Professor 

 Sabbatani in Cagliari, a paper published by his assistant, Dr. Regoli, in which the 

 latter shows that, while Ca and Sr diminish the irritability of the cerebral 

 cortex, Ba has the opposite effect ; EEGOLI, "Azione dei metalli alcalino-terrosi sulla 

 eccitabilita elettrica della corteccia cerebrale," Bollentino d. Societate tra i Cultori 

 delle Scienze etc. in Cagliari, Torino, 1901. 



