1893.] Correlation of Action of Antagonistic Muscles. 563 



end of the cutaneous branch of the hamstring nerve itself also 

 appears without effect upon the jerk. 



Tension produced in the crural triceps muscle by pulling on the 

 Achilles tendon does not appear to influence the brisk flexor move- 

 ment of the ankle joint evoked by tapping the subcutaneous face of 

 the tibia, and related chiefly to the 6th lumbar spinal segment of 

 Macacus and to the 7th lumbar segment of the Cat. 



It would thus seem clear that the exaggeration of the knee-jerk 

 produced by severance of the branches given from the great sciatic 

 nerve to the hamstring muscles is not due to the fact that the result- 

 ing relaxation of those muscles simply leaves the joint mechanically 

 more free to move. The exaggeration would seem due rather to the 

 severance of the nerves in question interrupting a stream of centri- 

 petal impulses that passes up from the hamstring muscles and enters 

 the spinal cord by certain afferent roots, and in the cord exerts a 

 depressing or restraining influence on the jerk. It further appears 

 that a stream of impulses similarly efficient can be set up by moderate 

 electrical excitation of the central ends of the divided nerves of the 

 hamstring muscles; or by simply stretching or kneading those 

 muscles when they are released from one of their fixed points ; or, 

 finally, by simply throwing those muscles into contraction through 

 excitation of motor roots supplying them, so long as the sensory roots 

 remain intact. The physician, when he, in order the better to elicit 

 the jerk, flexes the knee and reduces the strain in the flexor muscles, 

 by doing so removes, with relaxation of the flexors, a physiological 

 depression which the tension of those muscles normally exerts upon 

 the jerk obtainable from their antagonistic group. 



Further, it would seem that at the knee joint excitation of the 

 afferent fibres coming from one set of the antagonistic muscles 

 induces reflex tonic contraction of the opposing set with extreme 

 facility, despite the fact that the opponent muscles are not innervated 

 from the same spinal segments. The reflex is obtainable with extra- 

 ordinary facility, even across intervening segments of the cord. 



Thus the degree of tension in one muscle of an antagonistic couple 

 intimately affects the degree of "tonus" in its opponent, not only 

 mechanically, but also reflexly, through afferent and efferent channels 

 and the spinal cord. 



It is obvious that the correlation of action thus existing be- 

 tween the antagonistic muscular groups of the thigh and knee 

 may be not widely different from that originally pointed out by 

 Hering and Breuer as regulative of the movements of respiration. 

 One is tempted to institute a comparison also between it and the 

 physiological arrangement studied by Biedermann in the antagonism 

 of the muscles of the forceps of Astacus. I would, however, reserve 

 further details until I have been able to perform a larger number of 



VOL. LII. 2 P 



