Transmission-time of Reflexes in Spinal Cord of Frog 17 



comparatively strong reflex effects were obtained was not shorter than in 

 other normal preparations, nor in this preparation was it shorter the 

 stronger the effect. It was respectively, taking the four responses in order, 

 after allowing for transmission time in nerve (including that taken to 

 overcome the block under the kathode, which was in this preparation lo-) : 

 14-3cr, 13-9cr, 16-2o-, 13o-. The strength of the central stimulus, as estimated 

 by the strength of the effect it produces, is not therefore a function of the 

 time taken by the impulse to affect the motor cell. 



There is the same difficulty in making experiments with regard to the 

 influence of temperature on the time occupied in the normal cord, as with 

 strength of stimulus. On every occasion when, after an experiment has 

 begun, the gastrocnemius being used as indicator, I have either cooled or 

 warmed the back of a normal preparation, the reflex effect, if present 

 before, was no longer to be seen in records taken after such treatment. 

 In a few of the experiments I tried to make use of Biedermann's 

 experience that a reflex contraction could be obtained with greater 

 certainty in a cooled spinal frog if, after making the preparation, it was 

 given a long rest with a bag of ice applied to the spine. In eight 

 preparations, among which was the one which gave the lowest time value 

 for the cord delay, there had been for about half an hour, on the back of 

 the frog, a bag (an india-rubber finger-stall) containing ice. This was not 

 the case in the other experiments with normal cords, and it was in three of 

 these that the measured time interval between the two arrivals was longer 

 than 21cr, i.e. that the probable cord delay was over 19o-. The reflex time 

 in the experiments in which ice was used was not therefore universally 

 longer than in the experiments in which it was not. I do not of course 

 think that this proves that cold has no influence on the delay in the cord, 

 but I have npt yet been able to make an experiment that would either 

 prove it or disprove it satisfactorily.^ In the strychnised cord, which is 

 capable of giving a reflex effect a large number of times in succession, the 

 delay is most certainly increased by cold; but whether we should be 

 justified in applying, without reserve, to a normal preparation what we 

 know to be true of a drugged one is not, in my opinion, to be answered 

 straightway in the affirmative. 



The results obtained from the records taken in Exp. 37 (see p. 12) 

 make it appear that fatigue may have some influence on the time of the 

 cord delay. While in the first four responses this did not exceed (when 

 reduced) l7o-, in all of the last five it was over 18o-, and became finally as 

 long as 20(7. None of the other preparations gave evidence of this, but 

 with the one exception of Exp. 58 they all gave (or were allowed to 

 give) too few records of reflex effects to have been able to show it. This is 



1 I have now [Nov. 1907] made two experiments, using the biceps fenioris as indicator, 

 which show that the probable cord delay may become some lOo- longer in a normal cord by 

 a reduction of the temperature of the whole preparation from 12° C. to 6° C, and may agjun 

 become shorter when the temperature is raised once more to 12° C, though not regaining 

 its original value. 



VOL. I. — JAN. 1908. 2 



