64 Buchanan 



SUMMARY. 



By means of photographic records taken with the capillary electrometer, 

 it has been shown that : — 



1. The delay in the normal cord of the frog, in the same-limb reflex, as 

 determined by the interval of time between the two electrical responses of a 

 particular spot of a muscle (the gastrocnemius) when the efferent and afferent 

 fibres of the mixed nerve supplying it (the sciatic) were simultaneously 

 excited by a single break induction shock, varies in different preparations 

 between 0012 and 0022 second. It is very rarely as short as 0"012 second, 

 and only occasionally longer than 0-022 second. These numbers refer to 

 cord delay alone, time for transmission along the known length of nerve 

 having been deducted on the assumption that an impulse travels at the rate 

 of 30 metres a second along fresh frog's nerve. 



2. When the cord and the cord alone has been acted upon by a very 

 weak dose of strychnine, this delay is somewhat diminished. It then 

 varies in different preparations between 0'009 and 0'020 second at room 

 temperatures, though it is rarely as short as 0'009 second. It is seldom longer 

 than 0'020 second, except when the circulation as well as the cord has been 

 affected by the drug. In such cases the cord delay may become as long as 

 0"033 second, and the central stimulus may fail to exert its full strength 

 when it first begins to affect the muscle. 



3. Alteration in the strength of the artificial stimulus applied to the 

 nerve does not alter the delay in either the normal or the strychnised cord. 

 This statement is certainly true for stimuli above a certain strength (vary- 

 ing with the sensitiveness of the preparation), but probably does not apply 

 to stimuli the strength of which is only just above the threshold value. The 

 difficulties in the way of determining the threshold value for any one 

 preparation have so far prevented direct satisfactory investigation of the 

 effects of just adequate stimuli.^ 



4. Cooling the cord by applying ice to the back of the preparation greatly 

 increases the delay in the strychnised cord. Cold seems also to increase 

 to some extent the delay in the normal cord. 



5. Repeated stimulation (fatigue) may lengthen the delay in the 

 normal cord. 



6. The direct action of strychnine on the cord consists principally, so far 

 as the same-limb reflex is concerned, in making the discharge stronger, 

 and eventually longer, in response to a weaker stimulus. So far as the 

 crossed reflex is concerned, it also brings about something which before 

 prevented an effectual response from being obtained in the muscle to a 

 stimulus so brief as a single induction shock, applied to the sciatic nerve of 

 the opposite limb. 



^ A little direct evidence has, however, been obtained since this paper was written that 

 cord delay, even in the same-limb reflex, is longer when the strength of the stimulus is only 

 j ust adequate to produce a reflex response in the muscle. 



