202 ON MUSCULAR CONTRACTION. 



convulsions. The zinc becomes oxidized by the separa- 

 tion of oxygen from the fluid on the surface with which 

 it is in contact, whilst hydrogen gas is liberated at that 

 surface touched by the other metal. Here we have, in 

 the first place, a chemical change effected, then a pecu- 

 liar muscular disturbance. Each successive combination 

 or decomposition, like a pulsation, is transmitted along 

 the circuit from one extremity to the other. How the 

 impulse which is derived from the zinc is transmitted 

 through the body of the animal, or the tongue, to the 

 silver or copper is the next consideration. 



We can only understand this upon the supposition 

 that a series of impulses are communicated in the most 

 rapid manner along the connecting line ; the idea of a 

 current, although the term is commonly employed, tends 

 to convey an imperfect impression to the mind. It 

 would seem rather that a disturbance throughout the 

 entire circuit is at once set up by a series of vibrations 

 or impulses communicated from particle to particle, and 

 along the strange net-work of nerves. One set of che- 

 mical elements have a tendency to develope themselves 

 at that point where vibration is first communicated to 

 the mass from a better conductor than it is, and another 

 set at the point where it passes from the body to a better 

 conductor than itself. The cause of this is to be sought 

 for in the laws which regulate molecular constitution 

 by which chemical affinity is disturbed, and a new 

 attractive force exerted, in obedience to which the vital 

 energy is itself agitated. We must not, however, forget 

 that it is probable after all, although not yet susceptible 

 of proof, that the electricity does nothing more than dis- 

 turb or quicken the unknown principles upon which che- 

 mical and vital phenomena depend; being, indeed, a 

 secondary agent.* 



* Traite Experimental de T Electricite et du Magnetisms : 

 Becquerel, 1834, Priestley's Introduction to Electricity. On, 

 Electricity in Equilibrium : Dr. Young's Lectures. 



