132 Electricity and Galvanism, 



he succeeded in decomposing iodide of potassium, in directing the 

 needles of a galvanometer to 90°, and by aid of a condenser caused 

 the gold leaves of an electrometer to diverge. "When more delicate 

 tests of the electric current were made use of, their existence was 

 demonstrated in the muscles of all animals, and even of man himself. 

 Mr. Wilkinson, in his Elements of Galvanism, published in 1804, 

 calculated that the irritable muscles of a frog's leg were no less than 

 56,000 times more delicate as a test of electricity than that of the 

 most sensitive condensing electrometer. Mr. Wilkinson found that 

 two pieces of zinc and silver, each presenting a superficial surface of 

 — inch, produced violent contractions in the leg of a prepared frog ; 

 whilst two circular plates of zinc and copper required to be brought 

 twenty times in contact with the condenser, before any sensible diver- 

 gence of the gold leaves of an electrometer was produced. By 

 comparing the area of these plates, multiplied by the number of 

 contacts, with the superficial surface of the minute pieces of zinc 

 and silver employed to affect the frog's leg, he arrived at the con- 

 clusion I have just related. 



Prof. Matteucci availed himself of this circumstance in his contri- 

 vance of the frog galvanoscope. This is made by skinning the hind 

 leg of a frog, and separating it from the trunk, taking care to leave 

 as long a piece of sciatic nerve projecting as possible. The leg is 

 then placed in a glass tube, the nerve hanging over. In using 

 this contrivance all that is necessary is to let the piece of nerve 

 touch simultaneously in two places, the part where electric condition 

 is to be examined. If a current exists, the muscles of the leg will 

 become convulsed at the moment of contact. 



In this way the Professor detected a current in man, by making a 

 clean incision into the muscles of a recently amputated limb, and 

 bringing the nerve of the frog galvanoscope in contact at once with 

 the two lips of the wound, contraction instantly occurred. 



In pigeons and fowls, as well as in eels and frogs, currents were 

 readily demonstrable ; indeed, by alternating a series of the former 

 by approximating their sides, the raw surface of the muscles of which 

 had been exposed by a quickly made cut, Matteucci formed a sort of 

 battery resembling that made of the thighs of frogs. The result of 

 this experiment thus proved that energetic currents existed in hot 



