Rejlex Nervous Discharge. 



273 



repetitive discharge occurs not unfrequently when the stimulus is not 

 strong. Condition of the reflex centre rather than intensity of stimulus is 

 the decisive factor. 



II. 



A second point engaging us concerned the frequency of the rate of the 

 impulse-volleys of the reflex discharge in response to rhythmic stimulation 

 of the afferent nerve at various rates of frequency. A conclusion drawn by 

 previous observers* has been that, when the spinal centre receives successive 

 stimuli at rates of frequency greater than 10 a second, the motor centre 

 ceases to follow the rhythm of the stimulation. Its response is said to be 

 then of an independent rhythm rate, a rhythm proper to itself and 

 exhibiting a frequency of about 10 a second. The basis of this conclusion 

 was the observation that, below rates of stimulation of 10 a second, the 

 muscular contraction showed waves synchronous with the rhythm of 

 stimulation of the reflex channel, and that, with stimulations more frequent 

 than 10 a second, the muscular contraction exhibited, instead of undulations 

 synchronous with the stimulus rhythm, undulations, slight and somewhat 

 irregular, recurring at the rate approximately of 10 a second. This observa- 

 tion and conclusion were at variance with some earlier results by FranQois 

 Franck and Pitresf ; they were difficult to harmonise with certain experience 

 of our own in nerve-centres poisoned with tetanus-toxin. Hence the 

 necessity for re-examining the point in normal reflexes in order to confirm 

 or not its normal occurrence. For this our experiments have been with the 

 flexion-reflex of the hind-limb (cat), the preparation being spinal, the 

 popliteal trunk the afferent nerve, and the muscle tibialis anticus, the main 

 flexor of ankle. 



(1) The contraction was recorded isometrically, the myograph recorder 

 having a vibration period of about 0*01 i second. In the primary circuit of 

 the inductorium was a flat spring, whose vibration frequency, by alteration of 

 the length of the spring, could be varied readily between 10 and 60 a 

 second. The spring was armed with a fine style set close above a mercury 

 pool. We find the myograph of the reflex contraction exhibits clear 

 mechanical rhythm synchronous with the stimulation at rates up to 55 a 

 second, and sometimes beyond that. With rates up to 30 a second the 

 synchronous tremor is so coarse as to be obvious to the unaided eye. This 

 method of synchronous rhythm showed, therefore, in its graphic application, 

 that at frequency -rates up to somewhat above 55 per second, the rhythmic 



♦ V. Horsley and E. A. Schaifer, ' Journ. Physiol.,' vol. 7, p. Ill (1886). 



t F.' Franck and A. Pitres, 'Archives de Physiol.,' Ser. 3, vol. 5, p. 13 (1885). 



