328 



out the galvanic circle; which proves, that the nerves essentially consti- 

 tute the animal arc. To conclude, the galvanic circle may be entirely 

 animal: for this purpose, take a very lively frog, that is to say, .me en- 

 joying strong contractility: after insulating the lumbar nerves, present 

 these nerves to the thigh of the frog ; at the moment of contact, the limb 

 will be convulsed. Professor Aldini is the first author of this experiment, 

 which is really one of the most curious, as it leads more directly to the 

 explanation of the influence of nerves on muscular organs. 



There is no need that the nerves be untouched to allow the contrac- 

 tions, they are observed when these organs are tied or cut, provided there 

 be simple contiguity between the two ends made by the section. This 

 shows that no rigorous conclusions must be drawn from what happens in 

 galvanic phenomena, to what takes place in muscular action; since it is 

 enough that a nerve in man be cut or compressed by a ligature, to take 

 from the muscles to which if. is sent, the faculty of moving. I have, 

 however, observed, that disorganizing, by strong contusion, the nerve 

 which forms the whole or merely a part of the animal arc, interrupts, or 

 at least greatly impedes, the galvanic current. 



The epidermis obstructs galvanic action; which always is faint in parts 

 so covered. When it is moist, thin, and delicate, the interruption is not 

 complete; and hence the possibility is inferred of making on one's self the 

 following experiments. 



Lay upon the tongue a plate of silver, and a plate of zinc beneath; let 

 their edges touch, and you will feel a sharp t?,ste with a slight quivering. 

 Apply upon the eyes two pieces of different metals; make them commu- 

 nicate, and you will perceive sparks. Put apiece of silver in your mouth, 

 and a piece of tin into your anus, or copper, or any other metal; connect 

 them with an iron wire: the long hollow muscle, which, reaching from 

 the mouth to the anus, forms the base of the digestive canal, feels a con- 

 siderable shock: this has been carried to the length of exciting a gentle 

 purging, accompanied with slight cholic. Humboldt, after detaching the 

 epidermis from the nape of the neck, and the back, by two blisters, had 

 metals applied to the parts laid bare; and felt in each sharp prickings, 

 accompanied with a sero-sanguineous excretion, at the moment of com- 

 munication. 



You may construct the arc of excitation with three kinds of metal, or 

 two, or even one; with alloys, amalgams, or other metallic and mineral 

 combinations; with carbonaceous substances,* Sec. and it is observed, that 

 metals, which are in general the most powerful exciters, provoke con- 

 tractions with the greater success the larger surface they present. The 

 metals have more or less power of excitation: thus it is found that zinc, 

 gold, silver, and tin, hold the first rank; then copper, lead, nickel, anti- 

 mony, &c. without any apparent relation between their different degrees 

 of exciting power, and their physical properties, as their weight, malle- 

 ability, Sec. 



CLXXI. Galvanic susceptibility is like muscular irritability; it is ex- 

 hausted by too long exertion; and returns when the parts are left for a 

 time to repose. Dipping the nerves or muscles in alcohol or opiate 

 solutions, weakens and even will extinguish this susceptibility, in the 

 same manner, no doubt, as in the living man, the immoderate use of the 



* 1 employed successfully, in the winter of the year 1800, pieces of ice, both as sup- 

 ports and as communicators. 



