1909.] 



Innervation of Antagonistic Muscles. 



253 



And this holds good with the flexor muscle both in the decapitated and in 

 the decerebrate preparation. The view that strychnine, by lessening an 

 intracentral resistance, so allows the nervous impulse access where it 

 previously had none, is therefore hardly applicable to the flexor any more 

 than to the extensor : in both cases the effect is well explained by the 

 strychnine converting reflex inhibition into reflex excitation. 



II. — The algebraic summation of reflex excitatory and inhibitory effect 

 shows itself in the flexor muscle as well as in the extensor. Suppose reflex 

 contraction of semitendinosus to be in progress under faradisation of the 

 central stump of an afferent nerve, e.g., peroneal, of the ipselateral limb. If 

 then the central stump of an afferent nerve, e.g., popliteal, of the contralateral 

 fellow limb be suitably faradised, there ensues an inhibitory relaxation of the 

 contracting muscle. When the relative intensities of the stimulations of the 

 two nerves are appropriately adjusted, the contraction of the muscle is not 

 wholly abolished but is merely lessened in degree. The inhibitory stimulus 

 under these circumstances causes first a rapid partial lengthening of the 

 muscle, indicated by a descent of the myogram line ; this rapid descent 

 reduces the contraction to a certain level of diminished contraction, which 

 is then equably maintained during the further continuance of the inhibitory 

 stimulus, giving a plateau in the myogram. If, then, the inhibitory stimulus 

 be withdrawn, the excitatory still continuing as before, the reflex contraction 

 increases again forthwith, regains a higher level, and, subject to fatigue, 

 continues until finally the excitatory stimulus is itself withdrawn. That 

 this grading which involves inhibition as one factor can be accomplished in 

 either of two ways is proved by observation as follows : — Throughout a (fig. 5) 

 consecutive series of reflexes the excitatory stimulus can be kept of constant 

 intensity, while the inhibitory is varied in intensity in the sequent reflexes. 

 "When this is done, the amount which inhibition can subtract from the reflex 

 contraction is found to be graduable from the hardly perceptible up to 

 complete cancelling of all contraction for the time being. Conversely, 

 a series of reflexes (fig. 6), in which the inhibitory stimulus remains constant 

 in intensity but the excitatory is varied from reflex to reflex, produces degrees 

 of reflex contraction extending from hardly perceptible lessening of the reflex 

 contraction even to complete relaxation of the contracted muscle. 



With flexor motoneurones, therefore, as with extensor, a grading of reflex 

 contraction is obtainable by employing concurrently with reflex excitation 

 an appropriate reflex inhibition. The algebraic summation of these two 

 opposed influences results in an infinite series of grades of intensity of 

 contraction both in the extensor and in the flexor muscle. 



III. — The records show that the combining of any particular value of 



