Chap. XL] THE MUSCLE CURRENT. 117 



The needle will be suddenly deflected to one side, and 

 then will return to zero. Now, since copper is the 

 positive pole, the wire connected with it is + , and so 

 iiris known that when this wire is positive, the needle 

 will be deflected in a particular direction. Suppose 

 the deflection be to the right.1 then disconnect the 



O ' 3 



slips of copper and zinc, and connect the wire that 

 was positive to the trough on the right hand. Thus 

 it will always be known that when the deflection is 

 to the right, the trough on the right hand is positive ; 

 when the deflection is to the left, the trough 011 the 

 left hand is positive. 



To obtain the electrical current from living 

 muscle, take the adductor magnus muscle, or the 

 gastrocnemius, of the newly-killed frog. Make a 

 clean transverse section at one end, and lay the 

 muscle on the clay guards of the troughs, disposing 

 the plates of mica in such a way that only the middle 

 of the longitudinal surface is allowed to touch one 

 pad, and the centre of the transverse section the 

 other one. The troughs being arranged in short 

 circuit, open the key, and at once a great deflection 

 will occur, indicating a current from the muscle. 

 If the direction of the current be determined, it will 

 be found to pass out of the muscle by the longitudinal 

 surface. By making the surfaces touch opposite 

 cushions, the deflection will be reversed. By alter- 

 ing the position of the muscle, touching now two 

 surfaces and now two sections, the experiments may 

 be varied till the student has worked out for him- 

 self the various results given in the descriptions of the 

 phenomena in the text-books. The electrodes shown 

 in Fig. 59, and already referred to, afford the most 

 convenient means of studying the differences of 

 different points of the muscle. The muscle is laid 

 upon a perfectly clean glass plate supported on a 

 stand, and the finely-pointed ends of the clay talons 



