100 CORRELATION OF PHYSICAL FORCES. 



animal economy, we find that the first rationale given of the 

 convulsive effect produced by transmission through the living 

 or recently killed animal was, that electricity itself, something 

 substantive, passed rapidly through the body, and gave rise 

 to the contractions ; step by step we are now arriving at the 

 conviction that consecutive particles of the nerves and mus- 

 cles are affected. Thus the contractions which the prepared 

 leg of a frog undergoes at the moment it is submitted to a 

 voltaic current, cease after a time if the current be contin- 

 ued, and are renewed on breaking the circuit, i. e. at the mo- 

 ment when the current ceases to traverse it. The excitabil- 

 ity of a nerve, moreover, or its power of producing muscular 

 contraction, is weakened or destroyed by the transmission of 

 electricity in one direction, while the excitability is increased 

 by the transmission of electricity in the opposite direction ; 

 showing that the fibre or matter itself of the nerve is changed 

 by electrisation, and changed in a manner bearing a direct 

 relation to the other effects produced by electricity. 



Portions of muscle and of nerve present different electri- 

 cal states with reference to other portions of the same muscle 

 or nerve ; thus the external part of a muscle bears the same 

 relation to the internal part as platinum does to zinc in the 

 voltaic battery ; and delicate galvanoscopes will show electri- 

 cal effects when interposed in a conducting circuit connecting 

 the surface of a nerve with its interior portions. Matteucci 

 has proved that a species of voltaic pile may be formed by a 

 series of slices of muscle, so arranged that the external part 

 of one slice may touch the internal part of the next, and 

 so on. 



Lastly, the magnetic effects produced by electricity also 

 show a change in the molecular state of the magnetic sub- 

 stance affected ; as we shall see when the subject of magnet- 

 ism is discussed. 



I have taken in succession all the known classes of elec- 

 trical phenomena ; and, as far as I am aware, there is not an 



