86 CORRELATION OF PHYSICAL FORCES. 



in water, metal, or the oxide of metal, is forcibly detached, 

 producing great heat at the point of disruption, 



If we apply ourselves to the effect of electricity in the ani- 

 mal economy, we find that the first rationale given of the con- 

 vulsive effect produced by transmission through the living or 

 recently killed animal was, that electricity itself, something sub- 

 stantive, passed rapidly through the body, and gave rise to the 

 contractions ; step by step we are now arriving at the convic- 

 tion that consecutive particles of the nerves and muscles are 

 affected. Thus the contractions which the prepared leg of a 

 frog undergoes at the moment it is submitted to the voltaic 

 current, cease after a time if the current be continued, and are 

 renewed on breaking the circuit, i.e. at the moment when the 

 current ceases to traverse it. The excitability 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 trans- 

 mission of electricity in the opposite direction ; showing that 

 the fibre or matter itself of the nerve is changed by electrisa- 

 tion, and changed in a manner bearing a direct relation to the 

 other effects produced by electricity. 



Portions of muscle and of nerve present different electrical 

 states with reference to other portions of the same muscle or 

 nerve ; thus the external part of a muscle bears the same rela- 

 tion to the internal part as platinum does to zinc in the vol- 

 taic battery ; and delicate galvanoscopes will show electrical 

 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 magnetism 

 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 a 

 single electrical effect, where, if a close investigation be insti- 

 tuted, and the materials chosen in a state for exhibiting 



