258 Exptntr.tiitS tn the Irritation caufed by Hlnlalt 



die wound is covered with a plate of filver, and irritated by a rod of zinc, than when the 

 plate of zinc is placed on the wound, and the filver pincers are ufcd to eftablifli the com- 

 munication. 



When the communication is made by the conta^ of the epidermis, it produces no efFeft ; 

 it appears to inlulate like glafs, when interpofed between the wound and the metal : but if 

 the (kin be removed, by making two wounds at eight inches diftance, and a plate of zinc be 

 placed on one of them, and on the other a leg of a frog prepared, ihis lad is feen to contract 

 itfclf when it communicates with the zinc by the filver wire; which proves that the Galvanic 

 fluid then p.ini-s beneath the cpidormis. 



This fluid produced in fonic circumftances a verv fenfible acid tafle. The two wounds of 

 Mr. Humboldt having been covered, one with filver, the other with zinc, an iron wire of feveral 

 fcetin length.,attached to the ^inc,was conveyed between his upper lip and the fpongy fubflance 

 of the teeth, and thence to the tongue of another per fon. When the iron wire was made to touch 

 the fdver, a ftrongcontra£lion of the fcapular mufcle took place, and at the fame inllant the 

 pcrfon whofc tongue formed part of the chain of communication perceived the fenfation of 

 acidity. There are alfo cafes in which the fluid a6ls on the organs of ta(te without producing 

 any fenfible effect on the organs of motion : fu,.h is that where the epidermis ferves as the 

 conduQor from zinc to the frog ; for there is not then any contradlion, but merely an acid 

 tafte on the tongue. 



The author,having learned from Mr. Volta that he employed the folution of pot- afli (dkun 

 tartar! per dcliquium) in order to augment the conducting power, availed himfclf fuccefsfuUy 

 of this means to raife the capacity of the animal orgins. He moiftened one of his wounds 

 with this liquor, which produced little pain ; but the Galvanic irritation was more violent, 

 and accompanied with more heat ; fparks appeared and difappeared before his eyes ; tha 

 tongue nioiftened with the fan>e dilHndlly perceived the acid fenfation, although the com- 

 munication was eft.ibliflied only between zinc and zinc. The thigh of the frog, moilfened 

 with the alkaline folution and laid upon a plate of glafs, without touching either metal or 

 carbonic matter, fell of itfelf into violent convulfions, the antagonifl mufcles of the legs and 

 toes being inceflantly agitated. Irritability has been re-eftablifhcd by this application in the 

 animal parts, where it had been extinguilhed by warm folutions of the oxide of arfenic. 

 Laftly, the irritation (which does rtot commonly take place when the nerve and the mufcle 

 are armed with the fame metal, the different metals being between the coatings) becomes 

 manifell after this preparation ; which feems to indicate that the alkali not only irritates tlic 

 nerve, but llkewife adds to its irritability. 



The author applied this method to amphibious animals, which he roufed from their winter's 

 fleep, and m which he perceived a peculiar fymptom of irritability. 



Thefe obfcrvations led him to difi.inguifli two ftates of the animal organ. The firft, of 

 irritability naturally or artificially raifed or excited ; the fecond, irritability in a lefs degree. 

 Thcfe two ftates, which he calls pojilive and negative, are merely, as he remarks, different 

 degrees, and not phenomena abfolutely diftinft from each other. 



In individuals naturally fenfible, the effefts produced by alkaline folutions, by the oxy- 

 genated muriatic acid, by the folution of oxide of arfenic, are very rarely of the fame in- 

 tenfity. 



In the cafe of increafcd irritability, mufcular motions are obferved without metal or 

 5 carbonic 



