552 



HISTORY OF SCIENCE. 



of practical physiology, is shown on a larger scale in Fig. 263, where 

 a copper and and a zinc wire, marked respectively c and z, are seen 

 twisted together so as to insure contact. The copper wire touches 

 the crural nerves where these nerves issue from the spine. At the 



instant when the end of the zinc 

 wire touches the legs the muscles 

 exhibit a violent contraction. 



Galvani carried on his experi- 

 ments during a period of eleven 

 years before he published (1791) 

 his results and his views thereupon. 

 The sensation produced by the 

 publication of his work will be ade- 

 quately understood only by those 

 who are acquainted with the ideas 

 which were occupying men's minds 

 at the time. In many quarters Gal- 

 vani's views were enthusiastically 

 adopted, but dissentients soon ap- 

 peared who called in question the 

 physiological origin of the elec- 

 tricity. Singularly enough, Galvani 

 himself had at first been inclined to 

 attribute the origin of the electricity 

 to the metals, but he had abandoned 

 this theory as inconsistent with the 

 facts. A compatriot of Galvani's, 



named Alexander Volta, following up the observations made by Galvani 

 himself as to the greater energy of the contractions when the arc is made 

 of two different metals, opposed Galvani's theory by another in which 

 the contact of metals of different kinds was advanced as the origin of 

 the electricity. According to Volta, the facts proved that contact of 

 any substances of different kinds was a source of electricity; and the 

 contraction of the frog's legs, which took place when only one metal 

 was employed, was due to the contact of the metal with the humour 

 of the muscles. A memorable dispute arose. Galvani showed that 

 the intervention of a metal was not necessary to excite the contractions 

 it sufficed to cause the severed nerves to touch the exterior of the 

 muscle. He even brought forward an arrangement of the experiment 

 in which there was no heterogcneotis contact whatever. Notwithstanding 

 this apparently decisive instance, the contest was carried on for some 

 years, dividing the scientific world into rival camps. At length, in 

 1799, Volta, in pursuit of facts with which to support his own theory 

 of Galvani's experiment, was led to the construction of a piece of ap- 

 paratus which proved to be the point of departure for a new explora- 

 tion of the arcana of nature. No one invention was ever more fertile 



FIG. 263. 



