n8 



PHYSIO L OGICA L PHYSICS. 



[Chap. XL 



of the electrodes laid on different points of the muscle 

 to be examined, so that the position of the most 

 positive and most negative points of the muscle, etc., 

 can be discovered. 



Negative variation of the muscle current. 

 Fig. 60 represents diagramatically the arrangements 

 necessary for this experiment. On the right hand 

 and upper part of the figure are the troughs, with a 

 gastrocneinius muscle prepared with the sciatic nerve 



Fig. 60. Arrangements for Negative Variation 



attached. The muscle is laid with a transverse section 

 on one electrode, and a longitudinal surface on the 

 other. (The centre of each should touch the pad.) The 

 troughs are placed, through the intermedium of a key, 

 in connection with the galvanometer. The nerve is 

 laid across the platinum electrodes, which are 

 connected through a short-circuiting key with the 

 secondary coil of an induction machine, the primary 

 of which is in circuit through Wagner's hammer with 

 a key and a DanielFs cell. The needle being at zero, 

 the circuit of the troughs is opened, and the needle is 



