PHYSICS OF NINETEENTH CENT. ELECTRICITY. 549 



demonstrating to some of his pupils certain points in physiology, in 

 which recently killed frogs were the subjects operated upon. One 

 of them had been prepared for the purpose we have indicated, when 

 Galvani, having for the time to leave his laboratory, laid down the dead 

 frog near an electrical machine which some of his pupils were using at 

 the time for electrical experiments. During Galvani's absence one of 

 his assistants, in completing the anatomical preparations, happened to 

 touch the nerves of the frog's hind leg with his knife at the same moment 

 that one of the electrical experimenters was drawing a spark from the 

 machine. The legs of the dead frog made then a sudden convulsive 

 movement, to the great surprise of all present. Galvani was immediately 

 informed of the circumstance, and he hastened with eagerness to repeat 

 the experiment. The necessary conditions were soon recognized : when 

 one of the party touched one or other of the crural nerves of the frog 

 with the point of the knife, the corresponding leg was thrown into 

 violent action every time a spark was drawn from the conductor of 

 the neighbouring electrical machine. The frog or the person touching 

 it had, it should be understood, no direct connection with the electrical 

 machine, the result being, in fact, due to inductive action, or that 

 which is known as the "return shock." This incident is represented 

 in our engraving. Galvani, having discovered a new phenomenon, im- 

 mediately proceeded to investigate its causes and relationship by the 

 well-known experimental device of varying the circumstances. The 

 movement of the frog's legs occurred the first time the phenomenon 

 was observed at the touch of the dissector's knife. Galvani tried the 

 effect of touching the nerves with substances of different kinds, and 

 he soon found that any substances would produce the effect, provided 

 they were good conductors of electricity, and that the contact was 

 made in the neighbourhood of the conductor of the electrical machine, 

 and while a spark was drawn from the conductor. The next step was to 

 find whether electricity from different sources produced the same effect. 

 He tried the negative electricity of the machine, the electricity of the 

 Leyden jar, and that of the electrophorus. The same effect was observed 

 in all these cases. There remained only the atmospheric electricity. 

 Galvani instituted experiments on the effect of this also, by attaching 

 the prepared legs of a frog to the lower part of a wire which was con- 

 nected with a metallic rod elevated in the air. Violent contractions of 

 the frog's legs were observed whenever flashes of lightning appeared. 

 Galvani had now recognized the fact of the frog's legs being one of 

 the most delicate of electroscopes. And it was in studying the atmo- 

 spheric electricity by this new kind of electroscope, that he made the 

 capital discovery which appeared to confirm all his previous suspicions 

 of the action of electricity in vital phenomena. He had prepared a 

 number of these animal electroscopes, and by means of brass hooks 

 passed through the spinal cord, had them hung upon some iron railings. 

 He found that they exhibited contractions not only when flashes of 



