GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 135 



comparable to those observed in the active muscle. The electrical changes in 

 nerves are the only evidence of activity which we can observe, aside from the 

 effect of the nerve on the organ which it excites ; they are therefore of great 

 interest to us. 



Electrical energy, like all forms of active energy, is the result of a trans- 

 formation of potential or some form of kinetic energy. In the case of the 

 muscle, as of an electric battery, we find electricity to be associated with chemi- 

 cal change, and believe it to be liberated from stored potential energy. In the 

 case of nerves no chemical change can be detected during action, and hence we 

 are at a loss to explain the development of electricity. We can only say that 

 it is the result of some chemical or physical process which we have as yet failed 

 to discover. 



Although activity of nerve and muscle is found to be associated with elec- 

 trical change, we must not suppose functional activity to be in any sense an 

 electrical process. The movements of a man may be interpreted from the move- 

 ments of his shadow, but they are very different phenomena ; the activity of 

 the nerve and muscle is indicated by the electrical changes accompanying it, 

 but they may be independent processes. Certainly the irritating change which 

 is transmitted along the nerve and which 

 excites the muscle to action, although ac- 

 companied by electrical changes, is not 

 itself an electric current. 



Electrical energy is exhibited not only 

 by active nerve and muscle, but during 

 the activity of a great variety of forms 

 of living matter. It may be detected in 

 gland-cells, in the cells of many of the 

 lower animal organisms,* and even plant- 

 cells. The amount of electrical energy 

 developed in animal tissues may be far 

 from trivial. Although delicate instru- 

 ments are necessary to observe the elec- 

 trical changes in nerve and muscle, as 

 the great internal resistance of the tissues 

 causes the currents to be small, we find in 



certain fish special electric organs, which FIG. 58. Schema of galvanometer: n, s, north 

 i j'u j i j.' j and south poles of astatic pair of magnets; m, 



appear to be modified muscle-tissue, and mpensat g magnet> held p by ^0^ the 



which are capable of discharging a great staff, and capable of being approached to, or ro- 

 i ,_ i i , j tated with reference to, the suspended magnet ; 



amount of electrical energy when excited x> mirror . ft fibre supporting the magnets; c, c, 



through their nerves. So intense is the c, c, coils of wire to carry the electric current 

 . '' . . , near to the magnets, the upper coils being wound 



action OI this electrical apparatus that it ln the opposite direction to the lower ; e, e, non- 

 Can be Used as a weapon of defence and polarizable electrodes applied to the longitudinal 



surface and cross section of a muscle. 



offence. 



1. Methods of Ascertaining the Electrical Condition of a Muscle or a Nerve. 

 If the electric tension of any two parts of an object differs, the instant they are joined an 



