1913.] arising from Rivalry of Antagonistic Reflexes. 241 



{op. cit, fig. 1). By varying the conditions of experiment various transitional 

 forms can be obtained between imperfect irregular rhythmic movement and 

 the complete regular rhythmic series of movements constituting stepping. 

 Figs. 6, 7, and 15 furnish some illustration of this. 



III. 



Turning now to analyse some of the features of the rhythmic stepping the 

 example in fig. 1 may be used. The observation begins with stimulation 

 (faradic) of the right peroneal nerve, causing immediate inhibitory reflex 

 relaxation of the right knee extensor with synchronous reflex contraction of 

 the left fellow muscle ; both relaxation and contraction are perfectly steady 

 and arhythmic. After 2*5 sees., during which time the left muscle has 

 remained perfectly steadily relaxed and the right perfectly steadily con- 

 tracted, stimulation (faradic) of the left peroneal nerve is commenced, that 

 of the right still continuing unchanged. The steady relaxed condition of the 

 right muscle is at once broken by a contraction and at the same moment the 

 steady contracted condition of the left muscle is broken by an inhibitory 

 relaxation. The r. contraction and the L relaxation culminate synchronously 

 in about - 4 sec, and then die out about as rapidly as they appeared, to reappear 

 and similarly culminate synchronously again. In this way they rhythmically 

 and reciprocally appear and reappear in series so long as the concurrent 

 stimulation of the two nerves right and left is kept up, namely, for 6 - 5 sees., 

 seven complete steps being taken in that time by the extensor muscle 

 of each knee. The r. stimulus, the one commenced with, was then with- 

 drawn. The stepping immediately ceases in each muscle, except that the 

 r. muscle, which, having begun its stepping by contraction, is at the end of 

 the seventh step, relaxes, carries out a half-step more and passes into 

 steady contraction, thus assuming an attitude of full extension of knee ; 

 and that similarly the 1. muscle, which, having begun with relaxation, is at 

 the end of seventh step, contracts, executes a half-step more, passing into 

 relaxation and assuming a posture of flexion of knee. These final half-steps 

 and assumptions of reciprocal states at the two knees are, of course, due to 

 the action of the stimulation of the left nerve now remaining unopposed by 

 any concurrent stimulation of the antagonist right nerve. The 1. nerve 

 stimulation remains in operation until withdrawn 3 - o sees, later. During its 

 sole action no trace of rhythm appears in either muscle. On its withdrawal 

 the contraction of right muscle at once begins to decline, although, the 

 preparation being the tonic one, the " shortening reaction " of " plastic tonus " 

 has taken place, and the tonic shortness of the muscle still persists after 

 withdrawal of the stimulus. In the left muscle on withdrawal of left nerve 



