80 



PHYSIOLOGY 



CHAP. 



the sciatic nerve, with a synchronous photograph of the diphasic 

 current of action. In this case the muscle was indirectly stimu- 

 lated, and the contractile wave started from the end-plates which 

 usually lie about midway in the fibres, and spread from there 

 towards the two ends, one electrode connected with the sulphuric 



FIG. 56. Cardiogram of spontaneous beat of frog's heart, h, and simultaneous photograph of 

 diphasic variation, e. (A. D. Waller.) 



acid of the electrometer being applied near the middle of the 

 muscle, and the other, connected with the mercury, to the 

 tendinous end. Fig. 56 gives the spontaneous cardiogram of the 

 frog's heart with a synchronous photograph of the diphasic 

 variation, the sulphuric acid electrode being applied to the apex 



FIG. 57. Apparatus for leading off diphasic action current from the muscles of the human fore- 

 arm. (Hermann.) To right of figure an unpolarisable bracelet electrode ; r, r 1 , points of 

 stimulation of brachial plexus. 



of the heart, and the mercury electrodes to the base of the 

 ventricle. In the first experiment there is a positive oscillation 

 of the electrometer at the first phase, and a negative oscillation 

 at the second phase, because in the first phase the end of the 

 muscle is positive to its middle part, which was first thrown 

 into contraction negative to it in the second phase. In the 



