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Reciprocal Innervation of Antagonistic Muscles. Fourteenth 

 Note. — On Double Reciprocal Innervation. 

 By C. S. Sherrington, D.Sc, EES. 



(Received March 25,— Eead May 6, 1909.) 



(From the Physiology Laboratory, University of Liverpool.) 



I. — Reflex excitation and inhibition when brought to play simultaneously on 

 the motoneurones of an extensor muscle can be so balanced that there results 

 in the muscle a contraction, the degree of which evidences algebraic summa- 

 tion of the two opposed influences, the inhibitory and the excitatory.* This 

 summation is obtainable not only in the decerebrate animal but also in the 

 purely spinal (fig. 1). In the latter it proves obtainable in preparations quite 

 recently made spinal, for instance, after decapitation. This circumstance 

 much facilitates the physiological study of the phenomenon. In other words, 

 the grading (fig. 1) of reflex contraction of the extensor by varying intensity 

 of inhibition acting along with reflex excitation can be studied in the animal 

 freshly made spinal as well as in the animal in the decerebrate condition. 

 The muscle which I have chiefly employed in the purely spinal preparation is 

 the isolated extensor of the knee in the decapitated cat. 



A difference does indeed exist between the reactions of the preparation 

 in the decapitated and in the decerebrate condition. In the decapitated 

 preparation, as in the decerebrate, the reflex effect of any inhibitory afferent 

 is easily seen if stimulation of that afferent is employed concurrently with 

 stimulation of an excitatory afferent. If however the inhibitory afferent is 

 stimulated during the ordinary resting condition of the preparation, there is 

 usually no change in the muscle to show that the inhibitory afferent is pro- 

 ducing any effect at all (fig. 2). This is because the extensor muscle in the 

 decapitated preparation is not exhibiting tonus and lies relaxed, therefore 

 affording no background of contraction against which an inhibitory reflex can 

 reveal itself by causing relaxation. Even in this condition it can, however,, 

 easily be shown that the inhibitory afferent is then really producing a state of 

 inhibition in the preparation, although that state is not made evident by any 

 further relaxation. If a stimulus sufficient to cause reflex contraction of the 

 muscle be applied to the excitatory afferent while the inhibitory afferent,, 

 although apparently without effect, is being stimulated, the excitatory 

 afferent is found to be ineffective (or only partially effective) then ; but it. 



* Sherrington, ' Eoy. Soc. Proc.,' Note XIII, Nov., 1908. 

 VOL. LXXXI. — B. T 



