656 COMPARATIVE ELECTRO-PHYSIOLOGY 



in order that the intensity of the sensation may increase 

 arithmetically. The method of experiment on which this 

 result was based is not, however, altogether unexceptionable. 

 Against the generalisation itself, many objections have been 

 urged, and even its supporters claim for it only a very 

 limited range of application. It has been pointed out that 

 Fechner starts with the assumption that the change of 

 sensation under varying intensities of stimulus is merely 

 quantitative ; he does not take into account that the quality 

 or sign of sensation is also liable to change. 



Confining our attention to that range of sensation which 

 does not involve any change of quality, it is urged that, 

 starting from the minimally effective intensity of stimulus, 

 excitation at first increases very rapidly, and subsequently 

 more slowly, under successive equal increments of intensity. 

 This particular complexity led Fechner to suppose that such 

 complex phenomena as the quantitative relation between 

 stimulus and sensation were not determined by mere physical 

 or physiological factors. He therefore maintained that his 

 generalisation expressed an ultimate law concerning the 

 relation between physical stimuli and psychical reactions, 

 or, in other words, between body and soul. 



It is now possible, however, turning away from specula- 

 tive hypotheses, to subject this question to direct and simple 

 experiment. We have seen how delicate and free from 

 complication is the record of the mechanical response of 

 nerve. In these tracings we have the record of the direct 

 effect of stimulatory action on the nerve itself. In order, 

 then, to study the effect of stimuli of varying intensities, I 

 first chose a specimen of the sciatic nerve of gecko. A 

 sliding electric iriductorium was used for the purpose of 

 stimulation. From a previous experiment with a ballistic 

 galvanometer the absolute intensity of the electric shocks at 

 different distances of the secondary from the primary was 

 calibrated. Marks were then made on the sliding base, 

 which gave various intensities of stimulation I, 2, 3, 4, 5 

 and so on. Thus, keeping the duration of the exciting 



