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



reflex discharge must, therefore, with increase of the rate of stimulation of 

 the afferent nerve to heyond 75 per second increase to beyond 75 per second. 

 Whether that rate approaches actually near to the limit of the rate of 

 frequency which the reflex centre's discharge can follow cannot, of course, 

 be answered by this method. There is nothing to show that when in the 

 experiment the stimulation-frequency is changed from 75 per second to 150 

 per second, the reflex discharge does not, in fact, follow the latter figure, as 

 we may suppose the motor nerve to do in the case of its direct stimulation. 



The results by mechanical methods stand therefore no longer in contradic- 

 with those obtained by the galvanometer using oscillations traceable to 

 muscular action currents. C. Foa* followed in the chloralised dog action 

 currents of the contracting femoral quadriceps synchronous with the 

 electrical stimuli up to 20 per second, and in the frog up to 58 per second. 

 Beritofff concludes from galvanometric records that the discharge-frequency 

 of the flexion-reflex in the winter-frog may approach to 75 per second, and 

 in the summer frog to 150 per second, and P. HofimannJ that in the frog the 

 frequency may follow at first at 100 per second, though soon dropping to 

 half that number. With these our observations by mechanical registration 

 in the " spinal " cat are obviously perfectly compatible. 



The datum that the spinal reflex-centre is a mechanism constructed with 

 a recurrent refractory phase of lOOo- duration was irreconcilable with obser- 

 vations! tending to show that the duration of the spinal reflex-centre's 

 refractory phase is of an order not far removed from that of the nerve- 

 muscle preparation itself. The present results greatly relieve that difficulty, 

 for, although their method does not measure the actual duration of the 

 spinal refractory phase, they do show that the extremest length of that 

 phase does not, under ordinary circumstances, extend beyond 12cr. 



III. 



A third point requiring re-determination was the ratio between the 

 maximal power of the reflex tetanus and that of the peripheral tetanus 

 excited by faradisation of the muscle's motor nerve. The statement based 

 on direct experiment has been that the maximal power of the spinal reflex 

 contraction amounts to less than six-tenths of that developed by the 

 maximal contraction evoked by direct faradisation of the motor nerve.|| 



* ' Zeitschr. f. allg. Physiol.,' vol. 13, p. 35 (1912). 



t 'Zeitschr. f. Biol.,' vol. 62, p. 125 (1913) ; ibid., vol. 64, p. 161 (1914). 

 + ' Archiv f. Physiol.,' 1911, SuppL, p. 233. 



§ Sherrington and S. C. M. Sowton, ' Journ. Physiol.,' vol. 49, p. 342 (1915). 

 II V. Horsley, 'Brain,' vol. 21, p. 547 (1898). 



