1911.] 



Act of Progression in the Mammal. 



311 



has noted that the flexion reflex, for instance, is often terminated after 

 cessation of the exciting stimulus by an active phase of extension ; and that 

 the individual muscles which are in a state of inhibition during the applica- 

 tion of the stimulus contract suddenly after its termination. That this 

 phenomenon is not due to a proprioceptive stimulus generated in the muscles 

 which take part in that primary flexion reflex — or at any rate is not solely 

 conditioned by such a stimulus — is shown by Sherrington's observation* 

 that the rebound contraction — "successive spinal induction" — may be 

 obtained in the de-afferented preparation. 



Another point of interest and importance is the partial similarity of the 

 act of progression with that of the scratch. Sherrington! has noted this 

 similarity, and the present author^ has shewn that in the anaesthetised 

 rabbit the one state may immediately follow upon the other, and that there 

 is indication in some cases that the two may blend for a time. This partial 

 similarity is suggestive. Sherrington§ found that in the scratch-reflex the 

 flexion of the thigh did not completely relapse during each brief extension of 

 the phasic act — that there was always a certain amount of maintained 

 flexion. In certain states, as the present author || was able to shew for the 

 guinea-pig, the two factors in the scratch may be separated. And of these 

 two factors one is a state of maintained flexion while the other is a dis- 

 continuous inhibition of that state. In the scratching phenomenon described 

 by the present authorlT as occurring in the guinea-pig under anaesthesia there 

 is an alternation of the state of scratching from one hind limb to the other. 

 At any one time the state of maintained flexion complicated by rhythmic 

 inhibition is accompanied in the crossed hind limb by a state of maintained 

 inhibition of flexion. He has suggested that the rhythmic inhibition 

 during maintained flexion and the maintained inhibition of flexion which 

 immediately succeeds in the same hind limb may be expressions of one and 

 the same activity ; and that they may, in effect, be conditioned by variations 

 in the mutual influence of interacting spinal centres. The suggestion in 

 reality is that the locus of the inhibitory factor is central, and that it is not 

 of essential peripheral origin from proprioceptive stimuli. For the scratch 

 this is in accordance with a previous observation of Sherrington** that the 



* ' Q. Journ. Exp. Physiol.,' 1909, vol. 2, p. 109. 

 t ' Journ. Physiol.,' 1910, vol. 40, p. 28. 

 % ' Q. Journ. Exp. Physiol.,' 1911, vol. 4, p. 151. 

 § ' Journ. Physiol.,' 1906, vol. 34, p. 1. 



|| 'Q. Journ. Exp. Physiol.,' 1910, vol. 3, p. 21 ; ' Q. Journ. Exp. Physiol.,' 1911, vol. 4, 

 p. 19. 



1 ' Q. Journ. Exp. Physiol.,' 1910, vol. 3, p. 21. 

 ** ' Journ. Physiol.,' 1906, vol. 34, p. 1. 



VOL. LXXXIV. — B. 2 A 



