480 



Prof. C. S. Sherrington. 



[Jan. 31, 



Here the tempo of the stepping is also ahout 20 steps per 10 seconds, but the 

 stepping is strictly unilateral. 



These points argue that several sources of excitation probably co-operate in 

 the production of the stepping reflex. An important item in the execution of 

 the movement of the reflex in all its forms is flexion at the hip and knee. 



Suppose the " mark-time " reflex is in regular progress and is being recorded 

 from one knee, e.g., right by a thread passing thence to a pulley and light 

 lever, if then the other thigh (left) be gently supported from behind the knee 

 the record shows that the stepping reflex usually at once ceases in the right 

 limb (fig. 1. The reflex ceases entirely : the small undulations on the trace 

 in the interval during the cessation are due to swaying of the body, partly 

 respiratory, in the suspended attitude). The limb during the cessation of the 

 reflex hangs somewhat extended. On removing the slight support from 

 under the left knee the " mark-time " reflex at once recommences, with flexion 

 in the right knee. The reflex, on recommencing after this pause, continues as 

 it ceased, that is, its tempo and amplitude are practically the same as before 

 the interruption (fig. 1). 



This result contrasts with the following. Goltz and Freusberg* showed that 

 the " mark-time " reflex can be cut short by a strong squeeze of the tail. In 

 my experience this stimulus is best applied near the root of the tail. A 

 light touch on the hair of the tail often increases the stepping reflex, and the 

 stronger the mechanical stimulus to the tail the quicker and more powerful 

 as a rule is the inhibition of the stepping. But the stimulus to the tail need 

 not be very strong in order to cause inhibition. I judge that the intensity of 

 the mechanical stimulus which, applied to the tail, inhibits the reflex stepping 

 is such that, were the condition of the animal not spinal, would constitute a 

 dolorous (pathic) stimulus. The tail stimulus which inhibits may, therefore, 

 be considered adequate for a nociceptive reaction.f 



The application of this stimulus to the tail does not in any way interfere 



mechanically with the stepping movement. Suppose the " mark-time " reflex 



to be in regular progress and recorded as before, if then the tail stimulus be 



applied the stepping reflex is almost immediately arrested, and in both 



limbs. The reflex remains in abeyance while the tail stimulus is continued. 



On the cessation of the latter the reflex returns, and on its return soon 



shows indubitable increase in activity as compared with its activity before 



the inhibitory arrest (fig. 2). The increase is chiefly seen in the amplitude 



of the movement, but there is also often marked quickening of the tempo of 



the rhythm. I have seen the rhythm on some occasions quickened by 



* ' Pfluger's Archiv,' vol. 8. 



t ' Journ. of. Physiol.,' vol. 30, p. 39, 1903. 



