320 ELECTRO-PHYSIOLOGY. 



conceived the hypothesis of the electro-motive force, rejected the idea of Galvani 

 respecting animal electricity, and concluded that in all the experiments made 

 upon frogs the electricity was developed by the external arcs, because they were 

 heterogeneous, and that the animal did nothing but discharge it. 



Galvani opposed to these conclusions an experiment Avhich I have termed 

 capital, because it was, in reality, the point of departure of electro-physiology ; 

 that is, a true phenomenon of electricity developed by the living organism. The 

 experiment is this : The frog being prepared in the usual manner, a leg of the 

 same is bent so as to bring it into contact with the lumbar nerves. At that 

 instant the frog undergoes contraction, and this effect is repeated as long as the 

 frog is excitable, and each time that the contact is renewed. If the muscles 

 and the nerves continue to be kept in contact for a certain time, the contraction 

 often occurs even at the moment in which the contact is interrupted. 



Galvani demonstrated, as far as was then possible, by many sagacious and 

 well-conducted experiments, which were subsequently varied and extended, by 

 Humboldt and Aldini particularly, to other animals, that if the contact between 

 muscles and nerves was effected by means of interposed bodies, contraction 

 manifested itself only when those bodies were conductors of electricity, and that 

 it no longer occurred if isolating bodies were employed. Thus contraction re- 

 sults at the opening as well as closing of the circuit, if, the galvanoscopic frog 

 being held on an isolating surface, the extremities of the leg and of the nerve 

 touch a stratum of water or any homogeneous and conducting surface. Hum- 

 boldt used to place a portion of muscle between the nerve and the leg of the 

 galvanoscopic frog, and in this manner also contractions were excited. Aldini 

 observed the same fact discovered by Galvani in reference to the frog, by rap- 

 idly preparing in birds and rabbits the leg united with the sciatic nerve, and 

 folding that nerve on the muscles. Aldini further varied this experiment by 

 taking with the fingers the leg of a galvanoscopic frog, and bringing the nerve 

 into contact with the brain or the muscles of other living animals. As is 

 readily perceived, in thus operating he did but repeat the former experiments 

 of Galvani and Humboldt, with the difference that the arc between the muscles 

 and the nerves of the galvanoscopic frog was formed by the hand and by the 

 body of the observer, by the earth and by the animals touched with the nerve; 

 wherefore the contraction obtained in this manner could not be taken for a sign 

 of electricity in the animals touched. It was for this reason that I said, in one 

 of the preceding lectures, that it was proper, in using the galvanoscopic frog, to 

 support it with an isolating handle, and to touch the electi'O-motor which we 

 wish to study at two points of the single nervous fibre of the frog 



All these various forms of the leading experiment of Galvani left no doubt in 

 regard to the inference of the existence of a proper electricity of the muscles an.d 

 nerves in a state of life, nor was this demonstration in any manner contradicted 

 by the observation of Volta, viz : that the nerves and muscles represented the 

 two metals of the pair of plates, since it always proved that the nerves and 

 muscles act not as electromotors, if not taken in an animal living or recently 

 killed. 



In 1827, about fifty years after Galvani, Nobili, who had then improved the 

 galvanometer and rendered it very sensitive, made, with the frog prepared in 

 the manner of Galvani, the second capital experiment to which I have alluded. 

 Let us suppose we have the galvanometer with a long wire, and ou the astatic 

 system devised by Nobili, the extremities of M'hich are laminte of platina im- 

 mersed in two goblets filled vvith salt water. Before commencing the experi- 

 ment on the frog, Nobili takes a wick of cotton well steeped with the liquid and 

 unites with this wick the liquor of the two goblets. If the two lamiuoe of pla- 

 tina are homogeneous, a thing very difficult to realize, the needle remains un- 

 moved ; usually, however, there is deviation which results from the imperfect 

 homogeneity of the laminae, and especially from their having the secondary po- 



