1907.] Innervation of Antagonistic Muscles. 347 



gastrocnemius-soleus. The reaction then ceases on severing the afferent 

 spinal roots, through which pass the afferent fibres from the nerves of those 

 muscles. 



7. It seems possible that the diphasic result described in the following 

 section (Section VII) may likewise point to the admixture, in the afferent 

 nerves stimulated, of fibres provocative of opposite reflex effects (reflex 

 relaxation, reflex contraction) in the same muscle. 



VII. When the isolated vasto-crureus muscle with its nerve intact, or, 

 similarly, the isolated gastrocnemius, soleus, supraspinous or triceps brachii are 

 under examination for the reflex effect upon them of excitation of the afferent 

 nerves of their own limb, the inhibitory relaxation provoked is, on cessation 

 of the stimulus, very frequently followed at once by contraction (fig. 1). 

 This I have noted before,* but in systematically working through the 

 afferent nerves of the limb it is so usual a reaction as to demand further 

 mention here. It occurs with mechanical as well as with electric stimula- 

 tion. It occurs in reflexes excited from skin as well as in those excited 

 from isolated nerves, both cutaneous and deep. It occurs in the fore- 

 limb as well as in the hind-limb. It seems of central origin. 



Similarly, the inhibitory relaxation of the hamstring muscles, e.g., left, 

 provoked by stimulation of the central end of a nerve, e.g., vasto-crureus 

 nerve or plantar nerve, of the crossed hind limb (right), is sometimes 

 followed, on cessation of the stimulus, by an immediate rebound to 

 contraction in those muscles. This may be well seen after the nerve of 

 the corresponding extensors (left) of knee has been severed. A similar 

 result can be obtained from an afferent nerve, e.g., median, of the crossed 

 forearm (right). The stimulation of the median, giving inhibitory relaxation 

 of the hamstring muscles (left), is followed, on cessation of the stimulus, by 

 an immediate rebound to contraction. Again, under decerebrate rigidity, 

 when all the nerves of the hind limb (left) have been severed, excepting 

 only the nerve of the vasto-crureus, the reflex contraction of the vasto-crureus 

 excited by stimulation of a nerve, e.g., musculo-cutaneous, of the crossed 

 (right) forearm, is often followed, immediately on cessation of the stimulus, 

 by a relaxation of that muscle far more complete than that which existed 

 in it immediately prior to the reflex contraction. The phase of reflex 

 contraction seems here to be immediately followed by a phase of reflex 

 relaxation ; just as, conversely, in other cases the phase of reflex relaxation is 

 immediately followed by a phase of reflex contraction. 



The after-contraction following the inhibition seems best obtained when the 

 stimulus is not very strong, but appears more marked after moderate than 

 * ' Boy. Soc. Proc.,' vol. 77, B, p. 486. 

 VOL. LXXIX, — B. 2 C 



