272 Messrs. N. B. Dreyer and C. S. Sherrington. 



stimulus is much above threshold. More usually, however, the reflex con- 

 traction is more prolonged, and commonly also of greater height, which with 

 the isometric torsion myograph means of greater power, than is the maximal 

 twitch evoked by a single break-shock applied to motor nerve. This is 

 sometimes so when the break-shock stimulus used is not far above threshold 

 value ; it is almost always so, in our experience, when the stimulus, though 

 still of moderate intensity, is yet considerably above threshold value. The 

 same stimulus, as judged by position of the secondary coil on the inductory 



Fig. 1. — Contractions of tibialis anticus (spinal cat) in response to a single break-shock 

 stimulus, in B, C, E, F, applied to afferent nerve (popliteal), in A and D applied to 

 motor nei-ve (peroneal) direct. A, B, C, from one preparation ; D, E, F, from 

 another preparation. A and C, break- shock = 1000 units of Berne coil = 14 cm. 

 distance on scale ; B, at 500 units = 15"8 cm. on scale ; D and F, at 15 cm. on 

 scale = 750 units ; E, at 18 cm. on scale = 200 units. Top line, tuning-fork marking 

 0-01 sec. 



scale, gives reflexly a contraction more powerful and more prolonged than it 

 gives when applied to the motor nerve itself. At greater strengths still the 

 single-induction shock produces reflexly a contraction which may have a 

 height thrice as great and a duration seven or eight times as long as the 

 maximal contraction which it produced when applied directly to the motor 

 nerve itself. There can thus be no doubt but that a single momentary 

 stimulus applied to an afferent nerve often evokes a repetitive discharge of 

 impulses from the reflex centre to which that afferent nerve conducts. The 



