1906.] 



On Innervation of Antagonistic Muscles. 



491 



each inhibit one set of muscles and excite the muscles antagonistic to the 

 inhibited group. But in each case the reciprocal innervation has the same 

 direction, namely, excitation of the flexors and inhibition of the extensors. 

 This relation would obviously tend to make it more facile for flexion of 

 the limb to successively induce extension than for extension to induce 

 flexion. 



And another consideration has to be borne in mind. The measure to 

 which the intercurrent flexion-reflex exalts the following crossed extension- 

 reflex can be estimated in terms of the relation existing in the crossed 

 extension-reflex between intensity of exciting stimulus and intensity of 

 reflex response. A somewhat widely-expressed opinion is found in the 

 literature dealing with reflex action to the effect that intensity of reflex 

 response is relatively little determined by increase of intensity of exciting 

 stimulus (Wundt,* Hallsten,f Biedermann,J Baglioni§). Observations by 

 Merzbacherjl in the intact limb of the frog, and by Paril in the isolated 

 gastrocnemius, by myself** in the scratch-reflex, and by Langendorff ft m 

 the flexion-reflex of the tortoise, show that in some spinal reflexes at least 

 there can be obtained marked grading of intensity of reflex response in 

 conformity with grading of intensity of stimulus. In the extension-reflex 

 of the hind limb as obtained by stimulation of the opposite hind foot the 

 amplitude of the movement and its duration increase with increase of 

 intensity of the exciting stimulus. The relation between the intensity 

 of the stimulus and that of the response in this reflex is, in my experience, 

 somewhat different from that which obtains in several other reflexes, e.g., in 

 the direct flexion- reflex and in the scratch-reflex. The successive increments of 

 intensity of stimulus cause increase of the extension-reflex by fairly gradual 

 and regular degrees up to a certain point. Beyond that point relatively 

 larger increments of reflex response result from increase in intensity of 

 stimulation (fig. 7). This character of the ratio in this reflex between 

 increment of stimulus and increase of response is especially evident with the 

 after-discharge of the latter. In regard to the successive spinal induction 

 exemplified by the reflex, it is clear that if the intensity of stimulus chosen 

 for testing; the crossed extension-reflex be near below that value at which 



*, ' Untersuch. z. Mechanik d. Nerven u. NervenceDtren.' 



t 'Archivf. Physiol.,' 1885—1888. 



t ' Pfluger's Archiv,' vol. 80. 



§ ' Yerworn's Zeitschrift.' 



|| ' Pfluger's Archiv.' 



IT ' Archives Italiennes de Biol.' 



** ' Physiol. Soc. Proc.,' March, 1904. 



ft ' Sitzungsb. d. Naturforsch. Yersam.,' 1905. 



