256 



Prof. C. S. Sherrington. Break-shock 



That a reflex contraction is sometimes of the nature of a simple twitch, i.e., 

 non-tetanic, seems clearly shown by observations of Jolly (10) and of 

 Wertheim-Salamonsen (12) on the muscular action-current in the knee-jerk. 

 But the probability seems that the tetanic character so commonly observed in 



1,210 grm. 



450 grm. 



0-2 0-4" 

 Fig. 7. — Superposed tracings of photographic myograms all from same experiment 

 comparing those of greater crest-height than the maximal twitch, and indicating the 

 change in the height and duration relation when the break stimulation to the afferent 

 nerve (poplit.), is pushed to high strength, i.e., 14 cm. The lowest curve (m) is the 

 maximal twitch as given from 35 cm. up to 20 cm. The numerals opposite the other 

 curves give the coil-distance of the break-shock for each ; tibialis anticus, spinal 

 cat. Time or'dinates mark sec. : the drop of signal line at r shows latency for the 

 weaker reflexes, at m the latency for the motor twitches ; the faint line of drop 

 between these gives latency for the strongest reflexes. 



the reflex contractions dealt with in this paper, as evoked by a break-shock 

 applied to the bared aff'erent nerve, is, when that shock is of weak or moderate 

 intensity, referable to the reaction of the centre itself, and is, even when the 

 break-shock is stronger, still chiefly due to the centre. That is to say, even 

 when initiated by so brief a stimulus as a single induction shock, the reflex 

 action seems to involve some central process whose result is repetitive dis- 

 charge of impulses. The repetitive discharge of motor impulses is obviously 

 not to be thought of as more than the final outcome of the reaction in the 

 " centre." The relatively prolonged duration of that outcome and the long 

 central latency preliminary to it, together with other more general con- 

 siderations, suggest that underlying the discharge there is some central 

 process of other kind ; this underlying process need not, from the repetitive 

 nature of the discharge, be inferred to be itself repetitive, or if under some 

 circumstances rhythmically maintained, to be itself essentially rhythmic. It 

 finds expression through a mechanism (nerve-fibre) whose only mode of response 



