758 STUDIES IN GENERAL PHYSIOLOGY 
add from 2 to 5c.c. of a $m solution of Ca(NO,), to 100 c.c. 
of % NaCl solution, the margin at once begins its rapid 
beats. The only effect the addition of calcium has is to make 
the rate of the beats a little slower than without calcium. I 
thought at first that the stimulus of the wound caused by 
the cutting off of the margin might be responsible for these 
contractions in the presence of calcium. But this is not the 
case, for if we put a whole Gonionemus intact into any of 
these solutions, it behaves like the isolated margin. The only 
possible inference is that the margin is much more immune 
toward the inhibiting effects of calcium than the center, a 
fact which I have pointed out already in a former paper.’ 
In a pure CaCl, solution the margin will not beat. 
Inasmuch as the essential difference between center and 
margin which accounts for this difference in the effect of cal- 
cium is the presence of the central nervous system in the mar- 
gin, it may follow from these observations that for the supres- 
sion of twitchings of a nervous origin larger doses of calcium 
might be required than for the suppression of twitchings of 
muscular origin. Preliminary experiments on the motor 
nerves of frogs seem to harmonize with this idea. This sug- 
gests the possibility that, while a calcium treatment might 
be advisable for the cure of myogenic twitchings, for the 
suppression of neurogenic twitchings so much calcium might 
be required as to exclude the use of this remedy. This, too, 
is a point which further experiments on animals must decide 
before the matter may be tried in patients. 
III. THE PRODUCTION OF HYPERSENSITIVENESS OF THE SKIN 
BY ELECTROLYTES 
1. In a former paper I have shown that, aside from the 
rhythmical twitchings, the salts whose anions precipitate or 
inactivate calcium also make muscles and motor nerves sensi- 
1Part ITI, p. 692. 
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