Transmission-time of Reflexes in Spinal Cord of Frog 3 



by a submaximal stimulus of such strength as to give a curve of the same 

 height as the reflex contraction, and he thus obtained the result that the 

 delay in the spinal cord, together with the time taken in traversing part 

 of the dorsal roots, the ventral roots, and a small part of the sciatic nerve ^ 

 (a time which, he says, was too small to be measurable) varied between 

 0"008 and 0015 second. It is Wundt's lowest estimate of this same- 

 limb reflex time to which hitherto most importance has been attached. 

 As this seemed to be hardly justifiable, I have applied another method 

 which I regard as less open to objection (one which I had been using for 

 other purposes for several years in conjunction with Sir John Burdon- 

 Sanderson, by whom it was first introduced for measuring time relations 

 in physiological processes), to the purpose of determining the time-value 

 in question, and others in more complex reflexes. 



As indicator I have used, not the mechanical, but the electrical response 

 of a muscle, recording on a photographic plate, moving at a known and 

 equable rate, the movement imparted to the meniscus of the capillary 

 electrometer the moment an electrical change occurs at a spot connected 

 with this instrument. The fact that the electrical response in the organ, 

 as well as its manifestation in the recording instrument, occurs without 

 any delay as soon as the recording spot is reached, and that it is not 

 necessary for the whole muscle to be implicated before a record can be 

 obtained, obviates what seems to me to be the principal objection to 

 Wundt's experiments. The electrical response has the further advantage 

 over the mechanical response, for the measurement of brief time intervals 

 between different events occurring in a muscle, that the eflfect not only 

 begins without delay, but, when in existence, outlasts the stimulus (which, 

 either directly or indirectly, produces it) by a so much shorter time. A 

 second effect, therefore, occurring in the muscle only a few thousandths 

 of a second after a first, would have quite a distinct manifestation when 

 recorded by such an instrument as the capillary electrometer, whereas in 

 the record of the contraction of the muscle two such effects would be 

 merged into one. This being so, there should be no difficulty in recording 

 on the same photographic plate, and measuring the time interval between, 

 the two electrical effects produced at one and the same spot of the muscle 

 in response to simultaneous excitation of eflferent and afferent nerve 

 respectively ; nor is there any such difficulty, provided that the cord is 

 sufficiently sensitive for an effectual response to be obtained from it at all 

 when the stimulus applied to the aflferent nerve is single and instan- 

 taneous, as for the purpose in hand it must be. 



To eliminate any effect which the physiological or the physical condition 



' The frogs he used were large, being sometimes as much as 21 cm. long, so that 3 cm. 

 more of nerve may have been traversed in the case of the reflex response than was traversed 

 when the (ujjper part of the) sciatic nerve was stimulated. If one may infer, since it is 

 not otherwise stated, that he used the same species of frog and under the same conditions ot 

 temperature as were used for the experiments in the first part of his treatise, the species 

 was R. viridis, and the temperature between 15° and 17^° C 



