CHAPTER II. 



MUSCLE-NERVE. 



Appliances. Revolving drum; Myograph (heavy); Light muscle lever; 

 Inductorium; Moist chamber; Platinum electrodes; Non-polarizable elec- 

 trodes; Rheostat; Rheocord; Rheonome; DuBois keys (2); Pohl's commu- 

 tator; Glass plate for holding nerve; Cut-out key; Capillary electrometer; 

 Current interrupters; Signal magnets; 4 dry cells; Light copper wire; Va- 

 rious chemical reagents (see text below). 



I. STUDY OF ELECTRICAL APPARATUS. 



1. The Galvanic Current. Xhe fundamental experiment upon 

 which the principles of this form of electricity have been based was 

 unwittingly performed by Galvani in 1786. Galvani noted that 

 some frog's shanks, which had been hung by copper wires from an 

 iron railing and which were swinging to and fro, twitched when- 

 ever they came in contact with the railing. It is true that Galvani 

 misinterpreted the results of this particular experiment, ascribing 

 the phenomena to the development of an electric current within the 

 tissues themselves. That there are tissue currents, he did show by 

 later experiments. 



It was demonstrated, however, by Volta, a contemporary, that 

 Galvani's initial experiment was due to the production of a cur- 

 rent through completing the circuit between two metals of a differ- 

 ent potential. This constant flow of current between two sub- 

 stances of different potential has been called galvanic electricity, 

 in contradistinction to that form consisting of a single discharge or 

 a series of discharges from one body to another and where the cur- 

 rent is but of an instant's duration. The latter is known as static 

 electricity. 



The galvanic cell, as usually constructed, consists of two metals, 



