CHAP, iv.] PROPERTIES OF NERVOUS FIBRES. 399 



As to the action of electricity upon the motory nerves, it also 

 presents some interesting peculiarities. 



As a general rule, every interrupted current, or every strong 

 continuous current, applied to a motory nerve still in relation 

 with the muscles, provokes a muscular contraction, more or less 

 tetanic. 



On the contrary, the application of a feeble continuous current 

 causes one contraction at the moment of closing, and another at 

 the moment of opening. In the interval there is no appreciable 

 effect. 1 



According to M. Cl. Bernard the current acts only by 

 abruptly changing the electric condition of the nerve. In fact, 

 in certain cases, electricity causes the muscular contraction to 

 disappear. The galvanisation of the pneumogastric stops the 

 heart in the act of dilatation, of diastole. The tetanic con- 

 traction of a frog's foot, following the application of sea salt 

 to the nerve, ceases when the two points of galvanic pincers 

 are placed upon the lumbar nerve. Finally, all medical men, 

 however little acquainted with electro-therapeutics, know that 

 in man the passage of a continuous current often causes the 

 contraction of certain muscles to disappear instantaneously. For 

 our own part, we have several times had occasion to verify 

 this interesting fact. 



Long and very frequently reiterated excitations abolish, at 

 least for a time, the excitability of the nerve ; but if, for 

 example, we have employed a continuous current, it is then 

 sufficient to reverse its direction to awaken this exhausted con- 

 tractility, and the experiment may be repeated many times. 

 These voltaic alternatives, as they have been called, show plainly 

 that there is something altogether special in nervous motricity, 

 and that there exists in the inmost constitution of the axillary 

 cord a mobility, a molecular instability, which no other tissue 

 possesses. 



1 Vulpian, loc. tit., p. 71-73. 



