352 PROTOPLASMIC ACTION AND NERVOUS ACTION 



in pure NaCl solutions has been well known since 

 Sidney Ringer's time:^ this solution also causes rhythmi- 

 cal stimulation in motor nerve, although with a somewhat 

 prolonged latent period;^ in both cases the effect is 

 prevented by the presence of a little CaCla. The 

 muscle cells of marine animals are also powerfully 

 stimulated by pure isotonic NaCl; an especially instruc- 

 tive case is furnished by the larva of the annelid Arenicola, 

 in which the contraction in the pure NaCl solution is 

 very energetic. The body-cells of this organism contain 

 a yellow pigment which serves as an indicator of increase 

 of permeability. In the pure NaCl solution the pigment 

 diffuses into the surroundings simultaneously with the 

 contraction; and under a wide range of conditions the 

 permeability-increasing and the stimulating effects of 

 different salt solutions have been found to run closely 

 parallel. Thus both effects are prevented or diminished 

 by the addition of CaCla or MgCla to the pure Na-salt 

 solution; and the addition of organic anaesthetics in 

 the anaesthetizing proportions has a similar action.^ 

 Similarly pure isotonic alkali salt solutions cause activa- 

 tion and increase of permeabiHty in unfertilized starfish 

 and sea-urchin eggs, and both effects are prevented by 

 calcium salts or anaesthetics."* 



In general, any condition that prevents or retards 

 the increase of permeability normally produced by the 

 pure salt solution prevents or diminishes stimulation. 

 The anti-stimulating or narcotic action of compounds 



^ Cf. chap. viii. 



* Mathews, American Journal oj Physiology, XI (1904), 455. 



3 Cf. chaps, viii, ix. 



4 Cf. p. 166. 



