4 Buchanan 



o£ a particular piece of nerve excited might have on the time of arrival of 

 the response in the muscle, and to ensure that the two stimuli were applied 

 .■simultaneously, the simplest method to adopt seemed to be that of exciting 

 a mixed nerve at one and the same spot, by one and the same stimulus, 

 ■•so as to obtain in succession in the muscle, first the direct and then the 

 ireflex eftect. 



To be able to rely upon this method it was essential to know whether 

 or not there is any difference in the rate of propagation of an impulse, 

 -either through nerve, end-organ, or muscle, according to the strength of 

 the stiuuilus producing it; for the strength of the stimulus immediately 

 jproducing the reflex eflect could hardly be so strong in a normal cord as 

 .that which has to be artificially applied to the mixed nerve in order to 

 produce a reflex effect at all. With this object I made some preliminary 

 experiments on excised nerve-muscle preparations, and found that, with 

 a big resistance in the secondary circuit (as was employed in all the 

 experiments referred to in this paper, unless the contrary is expressly 

 stated), there is no difference — at least none that could be measured on 

 plates travelling at the rate of about 85 cm. a second — in the time taken 

 hy an impulse just strong enough to produce an effect at all, and that 

 taken by one strong enough to produce a " maximal " effect, when each 

 traverses in turn the same portion of a particular nerve and muscle — 

 provided, however, that the preparation was a sensitive one. In less 

 sensitive preparations a slight difference was occasionally manifested, but 

 one hardly amounting in any of my preparations to as much as a 

 thousandth of a second.^ As no electrical response to an excitation pro- 

 duced reflexly by the application of a single break induction shock to 

 afferent nerve can be obtained at all, except in very sensitive pre- 

 parations, there seemed therefore to be no need to use for comparison 

 with such response one produced by the application to the efferent nerve 

 of a stimulus of smaller strength, as Wundt had considered necessary. 



In the same and other experiments made with excised yjreparations, I 

 found, however, somewhat to my surprise, seeing that the exciting current 

 was of such brief duration, that the transmission time is appreciably and 

 very definitely affected by the direction of the induction current applied 

 to the nerve when this is at all strong, i.e. when it is nearly strong enough, 

 or just strong enough, to be felt on the tongue. A strength of excitation 

 so great as this was seldom used in my experiments. When used, the 

 extra delay, which sometimes even amounted to nearly two-thousandths 

 of a second, and always occurred in passing the spot to which the ex- 

 citing needle connected (indirectly) with the zinc of the battery was 



1 The difference, such as it is, when present, is probably one in end-organ delay, 

 since Engelmann (A. f. d. ges. Physiol., Ixvi., p. 574, 1897) has shown with the curarised 

 sartorins, excited by maximal and submaximal stimuli, that there is no difference in the 

 rate of propagation of the mechanical response in muscle, and Gotch (J. Physiol., xxviii., 

 p. 402) has shown that there is none in the rate of propagation of the electrical response 

 in nerve. 



