2 Buchanan 



were recorded, when, on the one hand, its sciatic nerve, and, on the other, 

 one or two of the posterior roots of this same nerve, were stimulated by 

 a single break induction shock. 



The question of the duration of this reflex time, and of the larger one 

 dependent on it, of the time taken to pass a synapse or neurone-junction,^ 

 is one of sucli importance, not only to the physiologist but to the psy- 

 chologist,^ that one ought to be very sure that the answer to it has been 

 supplied by methods which would be likely to give it correctly. 



Wundt's records were made on a pendulum myograph, the two curves 

 being on the same abscissa, and the difference of time taken, after the 

 moment of stimulation, for the muscle to begin to lift the lever in the 

 two cases, was measured. The difficulty in determining latencies with 

 exactitude by such a method is well known, but the chief objection to 

 which Wundt's experiments seem to me to be open is that he intention- 

 ally chose, for comparison with the reflex contraction, a contraction to 

 stimulation of motor nerve of equal amount, and therefore a submaximal 

 one, his reason for so doing being, that he found variations of direct latency 

 with varying strength of stimulus to be more marked than the differences 

 between the two kinds of latency.^ With the method he used of record- 

 ing the mechanical response, the increase of latency observed when the 

 stimulus to the motor nerve was submaximal instead of maximal was 

 probably * due to a smaller number of fibres being excited ; for those 

 excited, having the resistance of the whole of the rest of the muscle to 

 overcome, would fail to move the lever as soon as when all, or a greater 

 number of fibres are in action. It does not necessarily follow, and it seems 

 to me improbable (see p. 27), that the smaller contraction evoked when the 

 sensory root is stimulated owes its smallness to the same cause, so long 

 as no stronger contraction can be obtained by strengthening the stimulus 

 to the root. A further objection to Wundt's method is that, as he himself 

 had shown in an earlier work,^ the latency may vary a good deal with the 

 particular piece of one and the same nerve stimulated, and in his later 

 experiments the stimulus was applied to spots of different excitability^ 

 (loc. cit., p. 45). 



Wundt's experiments showed that the so-called "total latency," i.e. the 

 time which elapses between the excitation of the posterior root and 

 the beginning of the contraction of the whole muscle, varied in different 

 preparations'" between 0*025 and 0*050 second. From this time he de- 

 ducted what he found in each case to be the time which elapsed before 

 the whole muscle began to contract, when the motor nerve was excited 



1 Schafer(loc. cit.). 



2 See, e.g., M'Dougall, Brain, xcvi., pp. 588-9, 1901. 



3 Wundt, loc. cit., p. 16. 



* Judging from some experiments made in the Oxford Physiological Laboratory, of 

 which an account is given in the Journal of Physiology, vol. xxviii., 1902, p. 412. 



5 Wundt, Unters., etc., Abth. I. : Erlangen, 1871, pp. 192, 193. 



^ He says, " with the strength of the stimuhis," but none of the experiments of which 

 he has published the details seem to me to bear out this statement. 



