166 NATURE AND LIFE. 



Later researches have precisely fixed the conditions of 

 this influence of electricity upon the muscles. Continuous 

 currents, led directly to these organs, produce contractions 

 at the moments of opening and of closing the circuits ; but 

 the shock produced on closing is always the strongest. 

 While the continuous current is passing, the muscle re- 

 mains persistently in a half-contracted state, as to the na- 

 ture of which physiologists disagree. Influenced by ex- 

 citements rapidly repeated and prolonged for a short time, 

 the muscles assume a state of contraction and shortening, 

 like that seen in tetanus. In this state, as Helmholtz and 

 Marey have shown, the muscle suffers a repetition of very 

 slight shocks. Contraction is the result of the fusion of 

 these elementary vibrations, indistinguishable by the eye, 

 but capable of recognition and measurement by certain 

 contrivances. Currents of induction produce more power- 

 ful contractions, but not lasting ones, which are succeeded, 

 if electrization is prolonged, by corpse-like rigidity. Mus- 

 cular contraction effected in such a case is attended by a 

 local rise in temperature, proportioned to the force and 

 length of the electric action. This increase of heat reaches 

 its maximum, which may in some cases be four degrees, 

 during the four or five minutes following the cessation of 

 the electric impulse, and is due to the muscular contrac- 

 tion, which always gives rise to disengagement of heat. 



The effect upon the nerves is very complex, and be- 

 trayed by movements and sensations very variable in in- 

 tensity. Onimus and Legros state in general its funda- 

 mental laws thus : In acting on the nerves of motion, we 

 see that the direct or descending current works more en- 

 ergetically than the other, with the reverse result on the 

 nerves of sensation. The. excitability of those nerves of a 

 mixed kind is lessened by the direct and increased by the 

 inverse current. This is true as to battery-currents, but 

 currents of induction behave differently. While the sen- 



