Excitation and accommodation in nerve

Abstract When an electric current is passed through a living excitable tissue it changes the “condition” of the tissue in such a way that, if the change be in the right direction and great enough, excitation results. The “condition” is, as yet, of unknown nature: it may be an electrical potential difference: it may be an ionic concentration difference: various guesses at it have been made, but further evidence, and evidence of a more specific kind than that ordinarily considered in the theory of electric excitation, is required before a decision can be reached. The “condition,” however, has many analogies with a potential in the ordinary physical sense. It will be referred to as the “local potential” V of the excitable tissue: Keith Lucas (e. g., 1910) called it the “excitatory disturbance”: when we know better what it is, we can perhaps give it a better name. It will be denoted in general by V, and the resting value of V will be called V0. When a current is passed into an excitable tissue V is raised at the cathode, lowered at the anode: if V is raised enough, a state of instability is reached and “excitation” occurs. In a recent preliminary treatment of this subject (Hill, 1935, b) the name “cathode potential” was used. It was not realized at first that excitation at break of constant current fits into the scheme just as well as excitation at make: so that the anode must be considered equally with the cathode. “Electrode potential” has another meaning in physical chemistry and is therefore inadmissible. The changes considered occur, not in the body of the excitable cell, but around the points of entry and exit of the current. “Local potential,” therefore, refers to the condition at those points.