270 



Brevity, Frequency of Rhythm, and Amount of Reflex Nervous 

 Discharge, as indicated by Reflex Contraction. 

 By B. Dreyer and C. S. Sherrington, F.E.S. 



(Received May 31, 1918.) 



During an enquiry, for Surgeon-General Sir David Bruce's Committee on 

 Tetanus, into the neuro-muscular changes produced by tetanus-toxin, it 

 became desirable to re-examine certain commonly accepted data regarding 

 (he reactions of normal reflex-centres. 



I. 



The first of these that engaged us regarded the reaction of a spinal reflex- 

 centre to a single momentary stimulus applied to a main afferent nerve 

 playing on the centre. Evidence was desired as to whether the reflex 

 nervous discharge in response to the single volley of simultaneous centri- 

 petal impulses thus thrown into it consists similarly of a single volley of 

 emitted impulses, or whether it consists of a volley-series, brief but yet 

 repetitive, a series of volleys. The form of the reflex contraction should 

 throw light on this, when compared as to its space and time relations with 

 that of the simple muscle-twitch evoked by a like stimulus applied to the 

 motor nerve of the same muscle as that observed lor the reflex. 



That in certain cases the reflex response is a single- volley discharge is 

 extremely probable. The proprioceptive reflex of vastocrureus (" knee- 

 jerk")* and of tibialis anticusf appears to be simple twitches commonly 

 though not always. Using the same reflex as we ourselves turned to, Forbes 

 and GreggJ find that as evoked by a single break-shock the reflex nervous 

 response, as judged by its electrical effect, is often a single-volley discharge ; 

 they point out that dicrotism of the response need not mean that any 

 neurone discharges twice. On the other hand, the fact that,§ when the 

 single break-shock is strong, the reflex contraction may exceed in height 

 ■the maximal twitch obtainable direct through motor nerve suggests that 

 the reflex discharge is then, although brief, a repetitive volley-series. Beritoff|| 

 notes that in reflex tetani produced in the winter frog by strong faradisa- 

 tion at rates below 40 per second, some of the component shocks used as 



* Cf. W. A. Jolly, ' Quart. Journ. Exp. Physiol.,' vol. 4, p. 66 (1911). 

 t C. Asayama, ' Quart. Journ. Exp. Physiol.,' vol. 9, p. 265 (1915). 



I A. Forbes and A. Gregg, ' Amer. Journ. Physiol.,' vol. 37, p. 175 (1915). 

 § Sherrington and Sowton, 'Journ. Physiol.,' vol. 49, p. 331 (1915). 



II J. S. Beritofif, ' Zeitschr. f. Biol.,' vol. 62, p. 125 (1913). 



