CHAPTER XVI. 



GALVANISM. 



What is Gal- '^'^l- ELECTRICITY excited or produced by 

 tricuy?^'""'" *^^ chemical action of two or more dissimilar 

 substances upon each other is termed Gal- 

 vanic, or Voltaic Electricity, and the department of 

 physical science which treats of this form of electrical 

 disturbance is called Galvanism. 



What simple Thc most simplc method of illustrating the 

 luslrater'the productiou of galvauic electricity is by placing 

 gai'^rnfi°"eiec- ^ piocc of silvcr (as a coin) on the tongue, and 

 tricity? a piece of zinc underneath. So long as the 



two metals are kept asunder no effect will be noticed, but 

 when their ends are brought together, a distinct thrill will 

 pass through the tongue, a metallic taste will diffuse itself, 

 and, if the eyes are closed, a sensation of light will be evi- 

 dent at the same moment. 



This result is owing to a cliemical action wiiich is developed the moment 

 the two metals touch each other. The saliva of the tongue acts chemically 

 upon, or oxydizes a portion of the zinc, which excites electricity, for no chem- 

 ical action ever takes place without producing electricity. Upon bringing 

 the ends of the two metals together, a slight current passes from one to the 

 other. 



If a living fish, or a frog, having a small piece of tin- foil on its back, be 

 placed upon a piece of zinc, spasms of the muscles will be excited whenever 

 a metallic communication is made between the zinc and the tin-foQ. 



When and hoTT The productiou of electricity by the chemi- 

 Sectriclty^dTs- ^al actiou of two metals when brought in con- 

 coyered? ^.g^^^.^ ^^^ £j,g^ uoticed by Galvani, professor of 



anatomy at Bologna, Italy, in 1790. 



His attention was directed to the subject in the following manner: — Hav- 

 ing occasion to dissect several frogs, he hung up their hind legs on some cop- 

 per hooks, tintil he might find it necessary to use them for illustration, In 

 this manner he happened to suspend a number of the copper hooks on an 



