Electricity and Galvanism. 263 



falling to sleep ; and in a few cases these sensations have been suffici- 

 ently annoying to induce the patient to untwist the wires fixed to the 

 plate, when by interrupting the current these feelings ceased. But 

 if the plates were applied to opposite sides of the body, as when on 

 the chest to different sides of the mesial line, no contractions what- 

 ever occurred. This admits of explanation by a reference to the fact 

 of the nerves not crossing the middle line of the body. 



I have now repeatedly used this mode of exciting a purigenous sore 

 on different parts of the body, both in hospital and private practice, 

 and it has never in any instance failed ; I strongly recommend it to 

 your notice, where it is important to avoid the use of means more 

 alarming to the patient. I certainly know of no other plan by which 

 an equally effective discharge can be obtained, except by the use of 

 the moxa or actual cautery. 



As scientific and philosophic physicians, we must, however, go 

 a step further, and inquire into the rationale of this process : after 

 some little investigation, I traced it, as indeed was to be expected, 

 to the principles laid down in my second lecture, when endeavouring 

 to show how small an amount of electric force was sufficient to 

 tear asunder the elements of many compounds. 



In fact the saline ingredients of the fluid effused on the surfaces 

 of the blisters are decomposed, the sodium of the common salt being 

 set free at the silver surfaces, which by exudation, of course, rapidly 

 become soda : the chlorine is evolved at the zinc surface, forming 

 chloride of zinc. An electric current is then traversing from the 

 zinc through the interposed tissues to the silver, and back again to 

 the zinc, and its actual existence may be demonstrated by separating 

 the wires belonging to the plates and connecting them with a gal- 

 vanometer. I believe, therefore, the sore is really formed by the 

 escharotic action of the chloride of zinc thus produced, and the 

 reason why the patient feels none of the intense pain so characteris- 

 tic of the caustic energy of the zinc salt, is found in its acting in 

 infinitely small portions at a time upon the skin, — indeed, in what 

 may be correctly enough termed a nascent state. To prove this is 

 not mere hypothesis, I have placed on the table a vessel containing a 

 weak solution of common salt, having a tube closed at the bottom 

 with an animal membrane, and also containing salt and water im- 



