Voita on Animal EleSIricify. j57 



Ae double inimerlion of the bow. Clean both ends com- 

 pletely, and no agitation will arife, as in the firft experiment. 



For comparative experiments of this kind I would recom- 

 mend vifcous fluids or fubrtances rather than faline, becaufe 

 the latter are too foon dilfolved in tlie water. It oftimes hap- 

 pens that the convulfions of the frog, when it is completely- 

 prepared and highly irritable, take place, though both endi 

 x)f the metallic bow arc daubed over with the hniQ kind of 

 faline fluid. The caufe of thia is, that when one end is im- 

 inerfcd in the water after the other, (and it may be eafily 

 feen that it is inipoHible to do fo in a moment with fufficient 

 accuracy,) the one end of the bow lofes a portion of its faline 

 fubftance fooner than the other, or at lei^ft the adhering parfc 

 IS more diluted 1a' the water, fo that the fluid wjtli which 

 both ends have been daubed over is no longer the fame. 



For thefc experiments I would alfo recommend filver, as 

 a metal whch is Icfs liable than others to be attacked and 

 changed by faline and other liquids. Tin, lead, copper, and 

 in particular iron, are more fufceptible of laftjnp- variations ; 

 fo that bows of thefe metals, aj>d of ij-on above all, retain for 

 a long time the power of prodpciqg convulfions in a newly 

 prepared and highly irntablp frog, even whej> both the end^ 

 of the bow are immeifed in two glafles of water, although 

 the places of the nipta), attacked by any pf the faline fluids, 

 have been carefully waflied and cleaned, A fuperficial alte^ 

 ration in the nictal is fufiicjent to produce tliis change, as 

 may be e^fily feen. Thefe variations often fliew themfelves 

 to the eye hy a yellow blackifli fpot, &c. which it is difiicult 

 to remove. I do not hcrf; fpeak of lading variations, that 

 proceed to ;^ greater depth, which can be produced in the 

 end of the metallic bow, and particularly in iron, when ha 

 hardncfs iy changed j a procefs by which fuch a bow can be 

 rendered capable of producing not only convulfions in frogs, 

 but alfo a particular fenfation on the tongue, and light before 

 the eves, if both its ends, made perfectly clean, arc only 

 t)fouj;hl into coiitaa with pure water, Thefc, ?ind many 

 M 4 g^hr^- 



