Ig Buchanan 



It should here be noted that the strength of the direct effect was 

 appreciably altered in not a few of my experiments by the direction of 

 the induction current the break of which was used to excite the motor 

 nerve, even when the strength of the current was supra-maximal. The 

 steepness was in such cases more frequently less with the induction current 

 descending; but if several responses were recorded with the current in 

 either of the two directions alone, the direct effect was apt to be smaller 

 in a record afterwards taken with the direction reversed. The experiment 

 just referred to affords an instance of this : the first three responses were 

 to the break of ascending currents, the fourth to that of a descending 

 current. While in the second and third the direct effect was about as 

 strong as in the first, in the fourth it was very little stronger than the 

 reflex eftect on the same occasion. The direct effect obtained with the 

 descending current did not necessarily, when less in amount, begin to manifest 

 itself later, altliough sometimes, as in this instance, it did so. Such a 



Fig. 3. — First electrical response of the gastrocnemius 

 of a normal preparation obtained when the intact 

 sciatic nerve of the same side was excited by a supra- 

 maximal stimulus. [Time lines 730 per second.] 



difference in the strength of the effect (when it occurs) seems to me to 

 indicate some temporary impairment of the particular spot of nerve under 

 the anode, preventing perhaps the participation of the whole number of 

 fibres (in some cases the condition being brought about by this having 

 previously been a kathode), for in some of the preliminary experiments in 

 which the nerve was excited at two different parts of its length in turn, 

 the difference of the effect according to the difference of direction of 

 current might be marked when the one part and not when the other was 

 used. I have, however, made no serious attempt to understand the pheno- 

 menon, because it seemed to me to have little, if any, bearing on the matter 

 which is now concerning us. Moreover, the direct effect may get weaker 

 in the course of an experiment even without reversing the direction of the 

 current (see fig. 12 (E), p. 56). In none of my experiments (with the 

 possible exception of No. 49 ; see note to it on p. 42 ) was the strength of 

 the reflex effect altered by altering the direction of the induction current 

 applied to (the afferent part of) the nerve either in the normal or in the 

 strychnised cord. 



The probable cord delay in the one normal preparation from which 



