Transmission-time of Reflexes in Spinal Cord of Frog 29 



synapses) of the cord itself, or whether it is some indirect one, as, for 

 instance, on the oxygen supply to the cells. 



The fact that strychnine acts on cord delay in the opposite direction 

 to that in which fatigue would act, creates a difficulty in studying the 

 influence of this factor in strychnine preparations. Although Exps. 40 and 

 45, and the comparison of the two opposite same-limb reflex times in 

 Exp. 56, show that the times got longer as the experiment went on, both 

 Exps. 45 and 55 show that it was not shortened by rest ; so that I do not 

 think we should be justified in straightway attributing the increase of 

 length in the three experiments just mentioned to fatigue in the sense in 

 which this word is commonly employed. We shall see that this seems to 

 be otherwise in the case of the more complex I'eflex which we are going 

 to consider immediately. 



A way of investigating the eflect of fatigue on cord delay, or rather, 

 as I should prefer to call it, on synapse delay, which seems to me likely 

 to be fruitful, is that of recording long serial responses obtained from well- 

 strychnised preparations, and measuring the time intervals between suc- 

 cessive periods. For whatever is the ultimate source of the impulses which 

 give rise to the second and following periods,^ they must each in turn cross 

 the synapse forced in the first instance by the impulse transmitted through 

 the afferent nerve. It is well known that the periods may get longer towards 

 the end of such a response, if this is a long one ; but what determines the 

 duration of the response requisite for them to do so has not yet been 

 suflSciently studied. 



IV. The Same-Limb Reflex Time ix a Cord the Excitability of 



WHICH HAS BEEN RAISED BY PhEXOL. 



I have only as yet made two experiments with this drug.- As, however, 

 both show that the cord delay in the reflex we are studying was of the 

 same order as in the normal cord or in the strychnine cord, I think they 

 are worth referring to. Ten minims of a O'l per cent, solution, containing 

 therefore about 0-6 mgr., were injected subcutaneously two or three hours 

 before making the experiment. In the one preparation a reflex effect was 



' I still hold that this is to be sought in the central organ itself, and not in the peri- 

 pheral organs, as Baglioni (loc. cit., and Z. f. allg. Physiol., ii. p. 556, 1903) believes. 

 Besides the evidence against Baglioni's view brought forward by Sir J. Burdon-Sanderson 

 and myself (loc. cit. and Physiol. Centrall)l., 1902), there is the further objection that the 

 time between two successive periods is often not long enough (it may be as short as O'Oo 

 second) for an impulse not only to have got to the muscle and back to the cord, then back 

 again to the muscle, but for it to have made the muscle contract to such extent the first 

 time as to excite the sensory organs in it (or its tendon) and start the mipulse back to the 

 cord. Moreover, by Baglioni's method of treatment of the cord it is difficult to believe 

 that impairment of circulation would not have made cord delays longer than usual. 1 

 reserve, however, the discussion of the question for a later paper. As the text shows, it is 

 to something in the cord, other than the motor cell, that I would attribute the ]ieriodicity. 



- Since this jiaper was written I have made several, but as they all confirm what is 

 said here (and on p]>. 31 and 61), and as this paper is already too long, I must leave what 

 they have further to tell for a future communication. 



