The Characteristic of Nerve. 



209 



The number of the true minimal stimulus at optimum capacity and 

 voltage, is what I propose to designate as the characteristic, or other- 

 wise stated — the characteristic is the constant of the curve of the 

 smallest discharge of energy that can provoke movement, or of the 

 discharge of energy provoking greatest movement. 



By suitable adjustment of capacity and voltage we may obtain the 

 discharge of any desired energy — at any desired rate, if we also know 

 the resistance through which discharge is made. From a small con- 

 denser at high voltage, and from a large condenser at low voltage, we 

 may obtain the discharge (of equal quantities or) of equal energies, 

 but in the first case rapidly and in the second case slowly. We may 

 so adjust capacity and voltage, as to deliver constant energy in a 

 series of curves of varying steepness, and find by experiment the 

 more or less precise limits of steepness between which the motion or 

 excitation is greatest. The number denoting that steepness of energy 

 discharge by which a nerve is most economically mobilised, signifies 

 the optimum adaptation of excitation to excitability, and is its charac- 

 teristic. At that number the nerve is excited by the minimum of 

 energy. With a stimulus of higher or lower number, more energy is 

 necessary to produce an equal effect. 



Taking either a series of stimuli of given energy, but of varying 

 gradients, as in experiments 1 and 9, we are to observe at what gra- 

 dient the maximum effect is produced. Or as in experiment 2, making 

 a series of trials with varying amounts of energy from varying 

 capacity and voltage, we are to observe at what minimum energy 

 discharge the smallest perceptible effect is produced, and thence cal- 

 culate the characteristic. 



And even without actually determining the characteristic by means 

 of its upper and lower limits, we may often usefully ascertain whether 

 it is above or below a lowest or highest constant at the end of a series 

 of experimental data. Thus in experiment 6, a minimal energy has 

 not been reached, and we cannot therefore say that the characteristic 

 has been determined; we know however, that it is less than 10*4. In 

 experiment 4 the characteristic, as defined above, has not been actually 

 11382 and 0*6 since the stimulus has not been truly minimal; but 

 these values have been those of the constants of suitable stimuli not 

 far from minimal, and we know therefore that the characteristic has 

 been nearer to the higher value at high temperature, nearer to the 

 lower value at low temperature. 



a resistance of 100,000 ohms, and 1/n = |, the time of discharge of f of the original 

 energy is 000693 sec. If the voltage under -which this discharge takes place is 

 0*2, the original energy is 0"002 erg, and the number indicating its rate of discharge 

 is 174. If 0*01 mf. and - 2 v. should be the optimum capacity and voltage of a 

 minimal effect by excitation of a given nerve, i.e., a true minimal or optimal 

 minimal stimulus, then the number 174 is the characteristic of the nerve. 



