-6 ANIMAL ELECTRICITY. LECTURE I. 



and substituting in the circuit our own body for the 

 vessel of salt water, by laying one hand upon one 

 terminal, and a zinc rod held in the other hand upon 

 the other terminal. 



As before, you see that the current is from the zinc 

 through the body, and to the zinc through the galvan- 

 ometer, i.e., the zinc is electro-positive. 



You will find in this simple observation not only 

 a stepping-stone towards the proper understanding 

 of an animal current, but a ready practical device for 

 ascertaining in a complicated circuit what direction of 

 current at any part of the circuit is indicated by a 

 given deflection of the galvanometer. If you put 

 your body into circuit by taking one end of a wire in 

 one hand L, and touch the other end with a bit of 

 zinc, you will get the deflection indicative of current 

 in your body from the zinc, i.e., from R to L in the 

 figure. If that deflection is of the same direction as 

 that of the deflection under question, you know that 

 the latter was produced by activity on the R side ; 

 if the deflection is reversed, activity has been on 

 the opposite side. 



Our first representative experiment is a realisation 

 of the imaginary case that we took as our type, and 

 had best be shown to you at least twice, on the two 

 representative excitable, that is to say, living tissues — 

 on a muscle namely, and on a nerve. 



We will begin with muscle, with which the experi- 

 ment is easier to make and easier to understand. 



