1906.] On Innervation of Antagonistic Muscles. 495 



opposite phases of such cyclic reflexes as I have termed " alternating,"* and 

 shown to be particularly characteristic of the locomotor activity of the 

 mammalian spinal cord. If a reflex, A, not only temporarily inhibits the 

 action of an antagonistic reflex, B, but also as an immediately subsequent 

 result induces in arc of B a phase of superactivity, the central organ is in 

 that way predisposed for a second reflex opposite to A to occur in immediate 

 succession to A itself. Such an effect seems proved by the observations in 

 this and a preceding communication. A difficulty in applying it to the 

 case of an ordinary alternating reflex, e.g., the stepping reflex of the spinal 

 dog, lies in the intensity and long duration of the reactions which I have 

 employed in order to produce it experimentally. Such intensity and 

 duration certainly do not occur in the course of the alternating reflexes as 

 ordinarily observed. This, I think, does not exclude the likelihood that 

 successive spinal induction is a factor which does contribute to the 

 mechanism of alternating reflexes, although operating in smaller degree 

 than as exemplified in the intenser examples obtained under experimental 

 conditions and mentioned in this Note. 



Addendum, March 14, 1906. 



Since concluding the above I have met with marked successive induction 

 and rebound contraction following stimulation of the proximal end of one-half 

 of the split vasto-crureus nerve when the stimulus has been quite brief and 

 weak, i.e., has not been detectible to the tongue-tip, and has lasted only 

 from 1 to 2 seconds. Starting with the knee in semi-flexion, the stimulus 

 has caused immediate relaxation of the vasto-crureus (inhibition), followed, on 

 discontinuing the stimulus, by a rebound contraction, that has thrown the 

 knee into full extension. This result has been obtained with mechanical, 

 as well as electrical stimulation, of the nerve. It has also been obtained by 

 stimulation of the central end of the whole vasto-crureus nerve after total 

 severance of that nerve ; the extension then obtained is due to extensors at 

 hip and ankle, and guarantees that, in the rebound reflex, these latter 

 extensors, as well as the extensors of the knee, are thrown into contraction. 



The difficulty expressed in the concluding sentence above, of applying 

 successive induction and rebound contraction to explain natural " alternating" 

 reflexes, because of the lengthy and intense stimuli required to obtain them 

 experimentally, is therefore greatly lessened. An instance of distinct 

 rebound, induced by quite brief inhibition, is furnished in a figure 

 illustrating the notef on innervation of antagonistic muscles next preceding 

 * 'Phil. Trans.,' B, vol. 184, 1898. 



t 'Boy. Soc. Proo.,' vol. B, 76, p. 277, April 17, 1905, 8th note, fig. 3. 



