210 



Dr. A. D. Waller. 



Strictly speaking, the term minimal stimulus in, e.g., experiment 2, 

 applies only to the two values 0*001 134 erg and 0*002 erg in the two 

 groups respectively, since in these two cases only is the energy of 

 the stimulus at its minimum. 



But in accordance with ordinary tests by induction currents, the 

 term " minimal " is applied to stimuli that are certainly not of minimal 

 energy, but that produce minimal effects. And in this loose sense all 

 the trials of the above groups give minimals, in the first group mini- 

 mals of effective capacity at the several voltages, in the second group 

 minimals of effective voltage at the several capacities. 



The ambiguity may be provisionally neutralised by making use of 

 the expression " optimal minimal" for the true minimal stimulus qua 

 its energy value, and by avoiding use of the term minimal for stimu- 

 lation by induction shocks, or by condenser discharges of a gradient 

 above or below the optimum or characteristic gradient. 



The method followed will be most readily understood by considera- 

 tion of the diagram. 



(a) The apparatus for excitation, composed of battery, condenser, 

 and a Morse key, is connected with the nerve of a nerve-muscle pre- 

 paration by unpolarisable electrodes, the circuit being arranged so that 

 charge of the condenser is at contact a, and does not traverse the nerve, 

 while discharge is at contact b, and alone traverses the nerve. During 

 excitation the key Ki is closed, and the key K 2 open. 



(b) The apparatus for measurement of resistance, composed of 

 battery, Wheatstone bridge, and galvanometer, is connected with the 

 nerve by opening the key Ki (and closing the key K 2 ). 



To obtain fractions of a volt the disposition figured in the smaller 

 diagram! was adopted. 



