758 STUDIES IN GENERAL PHYSIOLOGY 



add from 2 to 5 c.c. of a fra solution of Ca(NO 3 ) 2 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. 1 

 In a pure CaCl 2 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- 



i Part II, p. 692. 



