Transmission-time of Reflexes in Spinal Cord of Frog 61 



preparation, it is almost always very weak, even when it subsequently 

 becomes strong, lends support to this view. If it is correct, it implies 

 that the probable cord delay (or extra cord delay, as the case may be) 

 given for each response in my tables represents the time taken to pass 

 the primary (or secondary) synapse by a sufficient number of individual 

 impulses at the same moment, to produce an effect on the muscle. They 

 therefore give the shortest time taken by a sufficient number of them 

 to pass simultaneously. When the effect is its strongest, as it usually 

 is, almost as soon as it begins, the probable cord delay given is the time 

 taken by the large majority, if not all, of the impulses arriving through their 

 several afferent channels to pass the synapse in that response. If any have 

 passed it more quickly, they were too few in number to produce an effect in 

 the muscle. Those that passed their synapses more slowly would only 

 produce an additional effect if a sufficient number of them do it in the same 

 time, and this apparently was only sometimes the case. 



That strychnine actually does make the time taken to pass the 

 individual secondary synapses get shorter, and does not only serve to 

 make them work more synchronously, seems to me to be attested by the 

 measurements of records in several individual experiments. If we may 

 express it in terms of what I have just ventured to set forth, these show 

 that the time taken by the greater number, the modal time, to borrow Pro- 

 fessor Karl Pearson's word,^gets shorter, not longer, as the drug becomes 

 more effective, and it would be most unlikely that those synapses which 

 can be passed in shortest time would be the last to be affected by the drug. 

 I hold, therefore, that the probable extra cord delays obtained from 

 records taken with strychnine preparations just so much affected 

 by the drug as to give a decided and definite crossed-ref lex response 

 at all, are likely to be those which would be obtained from each of 

 the cords when normal, could we from such a cord evoke a measurable 

 response ; and that the extra cord delays obtained from records taken at, 

 or very soon after, what we may call the critical moment in the action 

 of the drug, represent each the modal time (possibly also the average 

 time of the whole set) taken by the secondary synapses in any particular 

 normal cord. To know this modal time, the time taken to pass the greater 

 number of synapses, and to know the variations from the mode in any 

 particular set of synapses, seems to me far more important than to know 

 the shortest time in which a synapse may be passed. 



Another reason for the conclusion that the results obtained with 

 strychnine cords may be applied to normal cords is that, if the excitability 

 of the cord is raised by other drugs, the delay in traversing the cord, when 

 the nerve of the opposite side to the recording muscle is stimulated, is 

 longer than the delay when the nerve of the same side is stimulated, by 

 an amount of the same order as when strychnine was employed. This was 

 so in the two experiments I have so far made with phenol preparations.- 

 1 Phil. Trans., 186, Scries A, 1895, p. 345. - See footnote to p. 29. 



