LIFE AND FORCE. 



but the wider consequence was, that the world was 

 made acquainted, about the year 1786, with the fact 

 that an electric shock, communicated to a dead nerve, 

 would startle it into a temporary imitation of its 

 natural activity, in producing movement in the de- 

 pendent muscles. Swammerdam had in 1678 demon- 

 strated the same fact by another mode of experiment, 

 but this had neither been understood at the time, nor 

 remembered afterwards. This fact is usually shown 

 by means of a "nerve and muscle " preparation, that 

 is to say, a nerve trunk with its dependent set of 

 muscles, dissected out and isolated from the rest of 

 the body of a frog not long dead, in which it may be 

 clearly seen that the communication of an electric 

 shock to the nerve produces a twitching of the muscles, 

 more or less strong according to the force of the 

 current. But it must be. remembered, that, since the 

 same result ensues when the nerve trunk is stimulated 

 by giving it a poke, or by touching it with salt or acid 

 or some other irritating chemical substance, the fact 

 that the electric current will do the same does not in 

 the least prove that electricity has anything to do with 

 nerve force. 



The occurrence of certain electric currents, of 

 definite direction, in severed muscles, and of similar 

 currents in severed nerves, and the occurrence of other 

 definite currents when a nerve and muscle are put into 

 artificial activity, have led to various theories regard- 

 ing the connection of electricity with the motor forces 

 of the body; but most of these theories have now been 



