LECT. XII. XIII. BREGUET'S APPARATUS. 241 



periments I have made with this instrument, for the purpose 

 of determining the force of the contraction excited by the 

 electric current in different cases. But here are the general 

 conclusions at which I have arrived : 



1st. The contraction excited by the electric current, trans- 

 mitted along a nerve in the direction of its ramification, and 

 which we call direct, is always more energetic than that 

 which this same current produces when passing along the 

 nerve in the opposite direction. 



2dly. The direct current weakens and rapidly destroys 

 the excitability of a nerve ; whilst the passage of the inverse 

 current augments it within certain limits. 



3dly. To produce these effects, the action on the nerve, 

 of the direct as well as of the inverse current, ought to be 

 continued for a certain time, which will be longer in pro- 

 portion as the excitability of the nerve is weaker. 



It is very easy to prove, by experiment, the most impor- 

 tant of these conclusions; that is to say, that when the direct 

 current traverses the lumbar nerve of a frog for twenty or 

 thirty minutes, there are no further contractions, either when 

 interrupting or closing the circuit ; on the contrary, the con- 

 traction obtained by opening the circuit of the inverse cur- 

 rent, after many hours' passage, scarcely differs from that 

 which occurred at first, when the nerve was endowed with 

 great excitability This difference in the excitability of a 

 nerve, according as it has been submitted to the passage of 

 a direct or inverse current, can be observed whatever may 

 have been the manner in which the nerve is stimulated. 

 When we operate with the inverse current on a very ex- 

 citable nerve, and one which has never before been sub. 

 mitted to*the passage of the current, it is impossible to dis- 

 cover any difference between the contraction excited by the 

 opening of the circuit of this current after the passage has con- 

 tinued for one second, and that which occurs after the passage 

 16 



