1888.] 



NATURAL SCIENCES OF PHILADELPHIA. 



155 



RESEARCHES UPON THE GENERAL PHYSIOLOGY OF NERVE 



AND MUSCLE. 



BY Dr. HENRY C. CHAPMAN AND Dr. ALBERT P. BRUBAKER. 



No. 2. 



Resistance offered by Nerve and Muscle to the passage of an Elec- 

 trical Current. It was shown by the authors in a previous communi- 

 cation made to the Academy, No. 1, that both muscle and nerve are the 

 seats of electro-motive force amounting in the case of muscle to the 

 0*0696, of nerve to the 0*0237 of a Daniell, capable of deflecting the 

 magnet of a Wiedemann galvanometer as indicated by the scale to 

 an extent of 217 and 21 divisions respectively. Now since the 

 current after passing from the muscle or nerve to and through the 

 galvanometer, in returning to the point from which it started, must 

 pass through the muscle or nerve, it becomes a matter of importance 

 as well as of interest to determine the resistance offered by the latter 

 which must be overcome by the muscle and nerve current as the 

 internal resistance of the battery must be overcome in order that the 

 electrical circuit may be completed. The method made use of 

 by the authors in determining the resistance offered by muscle, 

 nerve etc. to the passage of an electrical current is that known as 

 the Wheatstone bridge method, a brief account of which is indis- 

 pensable to the proper understanding of the apparatus to be presently 

 described and by which the results to be communicated were ob- 

 tained. To illustrate the theory of the Wheatstone bridge let us 



T ^ suppose that a current 



from a Daniell element D 

 enters the wire A B Fig. 

 1 at A, the wire being 



A I m — ^ |b graduated into 1000 parts 



and along which the slid- 

 er S can be moved ; such 

 being the case if the slider 

 be pushed along the wire 

 Fig. 1. close up to A, then of the 



current entering at A, part returns through the galvanometer G and 

 part returns through A S B to the Daniell element whence it came. 



