Transmission-time of Reflexes in Spinal Cord of Frog 57 



fibres, and not all the same primary synapse cells were in play in the two 

 kinds of reflex response. In Exp. 55 all the records of the same-limb reflex 

 responses referred to with a f in the table had at the beginning the character 

 exhibited in the first of them (the one reproduced in fig. 11, A), while the 

 crossed-reflex responses more usually began in the way shown in fig. 11, B. 



At first sight the suggestion that some at any rate of the primary 

 synapses concerned may be different in the two kinds of reflexes may seem 

 to be incompatible with a suggestion I made before (p. 27) with regard to 

 the same-limb reflex response in the normal cord. It is, however, quite con- 

 ceivable that all the primary synapses and their cells, controlling the 

 particular muscle, may be brought into play when either sciatic alone is 

 stimulated by a strong induction shock, and yet that some come into 

 play more readily when the afferent fibres of the one nerve are excited, 

 others when those of the other are excited, and that such differentiation 

 takes place, though it may not always be manifest, when the exciting 

 currents are weak (even when strong enough to excite all the afferent fibres 

 of each nerve), or when certain synapses have failed to become, or to 

 remain, sufficiently responsive. The records obtained in Exp. 55, showino-, 

 as they do (see fig. 11), that neither reflex effect was ever so strong as 

 the direct, would lend support to such a view. The records obtained in 

 Exp. 56 might, however, at first sight seem to make it untenable, in so far 

 as they show that the reflex effects were, to begin with (fig. 12), about as 

 strong as the direct effect. But such a fact does not necessarily always 

 imply that all the muscle fibres have been excited by the stimulus coming 

 from the cord when this has had its excitability increased by strychnine. 

 The increased discharge which this drug enables the motor cells to give may 

 quite well so increase the strength of the eflect in the muscle fibres as 

 to obscure a small reduction in the number of fibres which are in plaj'-, 

 as compared with the number brought into play in the direct response. 

 That this is sometimes actually the case is shown, I think, by records 

 obtained in a few of my experiments (in 56 R amongst others) of same- 

 limb reflexes in which the direct effect was less strong than the reflex 

 effect. Occasionally it was so when the experiment began, as in the one 

 [Exp. 45] to which fig. 8, A, refers ; the curve derived from this record 

 would certainly show that the difference of potential when it first came 

 into existence in each response was somewhat greater in the case of the 

 reflex than in that of the direct response. Usually, as was the case in 

 Exp. 56 R, the reflex effect only became the stronger by the direct effect 

 becoming weaker (compare, in fig. 12, E with A or C). Since the one 

 muscle effect remained strong, the weakening of the other is likely to 

 have been due to some difference in the part producing the excitation, 

 i.e. in this instance in the motor part of the nerve, and the difference 

 seems to me to be most probably one in the number of fibres excited, 

 some of them having become in some way temporarily or even per- 



