1906.] On Innervation of Antagonistic Muscles. 



483 



which is so prominent a part of the mark-time reflex. The after-increase of 

 the latter reflex following on its inhibition by the tail-stimulus seems, as 

 shown above, a pure effect of rebound from inhibition. On the above view 

 it should show itself therefore chiefly in an after-increase of the flexion of 

 hip movement, and the graphic records of the effect show this to be the 

 case (fig. 2), the movement of flexion being the upward movement in the 

 tracing. 



This inhibition of the " mark-time " reflex exemplifies therefore the 

 principle of the common path* The reflex arc whose reaction is inhibited 

 and the reflex arc which inhibits are both found when separately examined 

 to use the same final common path, but to different effect. The common path 

 in this case is the flexor neurone of the hip, and one arc uses it in a steady 

 depressor manner and the other in a rhythmic pressor manner. The conflict 

 in this case, as so often, is between a nociceptive reaction and a purely 

 locomotor reaction ; and the former prevails as is usual, f 



The after-increase consequent upon inhibition is evidently a form of 

 " oahnung."% In order to distinguish it from those forms of " lahnuny " 

 which ensue without previous inhibition and are therefore immediate, it 

 may be conveniently termed " successive spinal induction," the more so as that 

 term draws attention to the likeness between the spinal process and certain 

 visual phenomena commonly designated " induction." 



Another instance of " successive spinal induction " is the following : In 

 the spinal animal (cat, dog) lying supine, the knee-jerk is elicited at regular 

 interval by tapping the patellar tendon. If, then, the central end of the 

 previously severed hamstring nerve is faradised, the knee-jerks become much 

 less ample or quite inelicitable. The tonus of the knee-jerk muscle (vasto- 

 crureus) is at the same time depressed. On discontinuing the stimulation of 

 the hamstring nerve, the knee-jerk quickly becomes again elicitable, and soon 

 is more brisk and ample than prior to the intercurrent inhibition§ (fig. 3). 

 The tonus also returns and in some cases becomes clearly greater than prior 

 to the inhibition. This after-increase of the knee-jerk takes place when, 

 during the whole period of inhibition, the leg is by mechanical support 

 prevented from drooping, and thus the passive stretch of the vasto-crureus 

 is avoided during the inhibition. The after-increase also occurs when the 

 elicitation of the knee-jerk is completely remitted during the whole period 

 of the inhibition. The after-increase is not therefore due to any continuance 



* Sherrington, ' Brit. Assoc. Reports, 1 1904, Address to Section I. 

 + Ibid. 



\ Exner, ' Pfliigers Archiv,' vol. 28. 

 § ' Roy. Soc. Proc.,' B, voL 76, p. 161. 



