TEAN8MI8SION OF THE SHOCK. 125 



stratum of water between the gold and the muscles? is more 

 than half a Hue thick. In the same manner, by employing 

 a conducting arc composed of two pieces of zinc and silver 

 soldered together endways; and resting, as before, one of 

 the extremities of the metallic circuit on the femoral nerve, 

 it is necessary, in order to produce contractions, to bring 

 the other extremity of the conductor nearer a ad nearer to 

 the muscles, in proportion as the irritability of the organs 

 diminishes. Toward the end of the experiment the slightest 

 stratum of water prevents the passage of the electrical cur- 

 rent, and it is only by the immediate contact of the arc with 

 the muscles, that the contractions take place. These effects 

 are, however, dependent on three variable circumstances; 

 the energy of the electromotive apparatus, the conducti- 

 bility of tlie medium, and the irritability of the organs which 

 receive the impressions: it is because experiments have 

 not been sufficiently multiplied with a view to these three 

 variable elements, that, in the action of electric eels and 

 torpedos, accidental circumstances have been taken for 

 absolute conditions, without which the electric shocks are 

 not felt. 



In wounded gymnoti, which give feeble but very equal 

 shocks, these shocks appeared to us constantly stronger on 

 touching the body of the fish with a hand armed with metal, 

 than with the naked hand. They are stronger also, when, 

 instead of touching the fish with one hand, naked, or armed 

 witli metal, we press it at once with both hands, either 

 naked or armed. These differences become sensible only 

 when one has gymnoti enough at disposal to be able to 

 choose the weakest ; and when the extreme equality of the 

 electric discharges admits of distinguishing between the sen- 

 sations felt alternately by the hand naked or armed with a 

 nu-tal, by one or both hands naked, and by one or both 

 hands armed with metal. It is also in the case only of 

 small shocks, feeble and uniform, that they are more sen- 

 sible on touching the gymnotus with one hand (without 

 forming a chain) with zinc, than with copper or iron. 



Resinous substances, glass, very dry wood, horn, and even 

 bones, which are generally believed to be good conductors, 

 prevent the action of the gymnoti from being transmitted to 

 man. I was surprised at no*: feeling the least shock o- 



