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Dr. C. S. Sherrington. 



" On the Innervation of Antagonistic Muscles. Sixth Note." By 

 C. S. Sherrington, M.A., M.D., F.E.S. Eeceived December 

 . 30, 1899,— Eead January 18, 1900. 



Machine-Hke regularity and fatality of reaction, although charac- 

 teristic of spinal reflexes, is yet not exemplified by them to such 

 extent that similar stimuli will always elicit from the spinal animal 

 similar responses. This want of certainty as to response is an 

 interesting difficulty attending the study of spinal reactions. The 

 variation in the responses of the skeletal musculature manifests itself 

 not only in regard to the extent of the movement but also in regard 

 to the direction of the movement. 



Some of the factors determining the character of the reactions are 

 factors contained within the stimulus. Important among these is the 

 " locus of the stimulus." Thus it has long been known that the direc- 

 tion and other characters of the reflex movement are influenced by the 

 mere location of the stimulus. Nevertheless stimuli identical in all 

 respects, including locality, may evoke reflex movements of widely 

 different, even of absolutely opposite, character. Such diff'erences of 

 response must be referred to diff'erences obtaining at the time in the 

 spinal organ itself. One cause for such diff'erences seems indicated by 

 the following observations : — 



The most usual, indeed the almost invariable, primary reflex move- 

 ment of the hind limb of the spinal dog (and cat), when spinal transec- 

 tion has been performed in the cervical or upper thoracic region, is 

 flexion at hip, knee, and ankle ; the limb is " drawn up." This move- 

 ment can be well obtained by, among other stimuli, the pressing of the 

 pads of the digits upward so as to extend the toe-joints, a stimulus 

 that in some measure imitates the eff'ect upon those joints of the 

 bearing of the foot upon the ground under the animal's weight. 

 Extension as a reflex result from this stimulus is, in my experience, 

 never met with in the homonymous limb in the early time after transec- 

 tion. "When a certain period has elapsed, three weeks or more after 

 transection, and shock has largely subsided, it becomes possible to, at 

 times, obtain extension at hip as the primary movement in the 

 homonymous limb. The pressing of the toe-pads upwards, spreading 

 and extending the digits, elicits a sharp movement of extension at the 

 hip, if at the time the initial posture of hip and knee be flexion. If 

 the initial posture of hip and knee be extension, the primary reflex 

 movement excited is, in my experience, invariably flexion. The 

 reflex movement is, it is true, not unfrequently flexion, even when the 

 initial posture is one of flexion ; but it is, on the other hand, very 

 frequently, and especially preponderantly in certain individual animals, 

 extension. The passive assumption of a flexed posture at hip and 



