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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 % NaCl solution 
+ 8c.c. of aSmCa(NO, ), solution no contractions occurred. 
A series of experiments with a slightly greater amount of 
CaCl, 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. % NaNo; 
100c.c.% NaNo;+ lec. m BaCl, 
100c.c.% NaNos;+ 2c.c.m BaCl, 
100 c.c.% NaNo;+ 4c.c, m BaCl, 
100 c.c.% NaNo; + 8c.c. m BaCl, 
100 c.c. % NaNo; + 16c.c.m BaCl, 
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.’ 
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- 
1Since 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 onposite effect ; REGOLT, “Azione dei metalli alcalino-terrosi sulla 
eccitabilita elettrica della corteccia cerebrale,” Bollentino d. Societate trait Cultoré 
delle Scienze etc. in Cagliari, Torino, 1901. 
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