14 Buchanan 



was 



descending, it took the impulse V'la- to overcome the obstruction under 

 the Zn electrode on its way to the milscle. Hence, although the reflexly- 

 produced impulse actually arrived at the muscle ISTa- later, the difference 

 between the two times of arrival would have been 14>-9ar, had it not been 

 for the delay to the direct impulse, unless, as is not at all improbable, the 

 obstruction was still there (in an attenuated form, i.e. causing a shorter 

 delay) when the reflexly-produced impulse reached the same spot later, in 

 which case it would have been somewhat shorter. That it did so persist is 

 one alternative suggested by the preciseness with which the measured time 

 taken for the reflex effect to reach the muscles recurred alternately with 

 the ascending and descending current in the first four responses. Instead 

 of reaching the muscle l-2(r later, when the current was ascending, as one 

 might have expected, it reached it only Q-Qcr later than when it was 

 descending (in IQSa- in the one case, IS'To- in the other). Allowing Olo- 

 for the extra 4 mm. of nerve which w^ere traversed by it in the former case, 

 and granting that the obstruction persisted, the whole time taken to reach 

 the muscle was therefore not more than O'So- longer when the impulse met 

 with the block at the start (current ascending) than when it met with it 

 first on its return from the cord some 2 -So- later (current descending). 

 Assuming, as one can hardly help doing, that the delay at the outset at one 

 spot when the current is going in one direction is the same as it is at 

 another spot 4 mm. away, when the current is going in the opposite direction, 

 it looks either as though the reflex effect were delayed O'To- on its way to the 

 muscle when the current was descending, and not delayed at all on its way to 

 the muscle when the current was ascending, in which case the cord delay 

 would be 14*9cr — 0-7(T— 2*5cr = ll'7cr; or as though the impulse produced 

 by the ascending break induction shock was accelerated when it had to 

 pass a second time, but in the reverse direction, the spot at which it had 

 before been delayed, in which case the cord delay would be 14-9(t— 2-5o- = 

 12-4(7, and the supposed accelerating factor would be such as to make the 

 impulse traverse the spot O'lcr more quickly than it would otherwise have 

 done. Not knowing which of these alternatives, or what other alternative, 

 best expresses what actually occurred, I have in such experiments (showing 

 kathodic obstruction) given a value to the cord delay intermediate between 

 the two which it seems to me that it might have (see above). The error so 

 introduced is hardly greater than another error which could not be avoided, 

 that, namely, which arises from the assumption made that the rate of trans- 

 mission along nerve where there is no block, is the same for all nerves and 

 at all temperatures, i.e. all at which my experiments have been made 

 (11° C.-18° C). But neither solving the doubt nor removing either error 

 would alter the absolute value of the cord delay by more than a fraction 

 of a, and would not alter the relative value in successive responses in any 

 one preparation at all ; at any rate not in such of them as were taken with 

 the induction current in one and the same direction. 



