GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 141 



change at the part where the tissue is dying, and called by Sanderson " the 

 diminutional effect." This continuous negative change is probably attributable 

 to the presence of a continuous contraction process, perhaps the contracture 

 which we observed in studying the tetanus curve (see Fig. 49). This " dirainu- 



FIG. 62. Record of changes in electric potential in a tetanized injured muscle of a frog. The leading- 

 off non-polarizable electrodes connected with the capillary electrometer touched the normal longitud- 

 inal and injured cut surface of the muscle. The muscle was tetanized by an induction current applied 

 to its nerve, the rate of interruptions being 210 per second. A rise of the curve indicates an electrical 

 change of opposite direction to that caused by the injury. The diminution of the current of injury, 

 which was less than in some other experiments, was 0.008 volt. The time record at the bottom of the 

 curve was obtained from a tuning fork making 500 double vibrations per second (after Burdon San- 

 derson). 



tional effect " is only to be observed upon an injured muscle, since it repre- 

 sents a difference in potential between the normally contracting and the injured, 

 imperfectly contracting muscle-substance. When all parts of the muscle are 

 normal and contracting to an equal amount, the electrical forces would be 

 everywhere of the same nature, balance one another, and give no external 

 evidence. Although the dimiuutional effect is only to be observed upon the 

 injured muscle, the temporary negative changes which follow each excitation 

 are to be observed on the normal muscle. To understand this we must con- 

 sider the diphasic current of action. 



Diphasic Current of Action. If a normal muscle be locally stimulated by 

 a single irritation, either directly or indirectly through its nerve, the part 

 excited will be the first to become active and electrically negative, and this 

 condition will be taken on later by other parts. Our methods only permit us 

 to observe the relative condition of the parts of the muscle to which the elec- 

 trodes are applied, the changes in the intermediate tissue failing to show them- 

 selves. If an electrode be applied near the place where the uninjured 

 muscle is stimulated, A, and another at some distant point, B, and these 

 electrodes be connected with a capillary electrometer, a diphasic electrical 

 change will be observed to follow each stimulation. At the instant the irritant 

 is applied the muscle-substance at A will become suddenly negative with 

 respect to that at B; when the spreading irritation. wave has reached B, that 

 part too will tend to be negative, and an electrical equality will be temporarily 

 established ; finally, B continuing to be active after A has ceased to act, B 

 will be negative in respect to A. Since the wave of excitation spreads along 

 the fibres in both directions from the point irritated, each excitation will cause 

 two such diphasic electrical changes. 



