Comparisons between Reflex Inliibition and Reflex Excitation 



69 



abductors and internal rotators of hip express the excitatory ( + ) side of 

 the reflex, by contracting ; extensors of hip, knee, and ankle, and adductors 

 and external rotators of hip express the inhibitory ( — ) side of the reflex 

 by relaxing. To serve as samples of these opposed groups reacting under 

 the reciprocal reflex innervation, two muscles were chosen, which act on 

 one and the same joint, but oppositely. These were semitendinosus as 

 flexor of knee, vasto-crureus as extensor of knee. The reflex preparation 

 was made as in previously reported observations,^ deep chloroform narcosis 

 being employed until after the destruction of the brain. 



The reflexes obtained from the isolated semitendinosus show clear 

 grading of intensity of contraction following grading of intensity of the 

 break shock, figs. 1 and 2.- The grading, even under experimental 

 conditions, is sufficiently delicate and covers a sufficient range of gradation 

 of stimulus to indicate that under natural conditions strength of stimulus 

 must influence minutely and widely the extent and force of the actual 



Fig. 1. 



movement in the flexion-reflex of the limb. This result is welcome, because 

 it conforms with what would be expected from the standpoint of teleology. 

 In the examples figured (figs. 1 and 2), the sequence of change of intensity 

 of the external stimulus has been from weaker to stronger. The grading 

 of the reflex response has, however, been equally obvious when the direction 

 of the sequence has been reversed. A feature noticeable in the myograms 

 is that not only does the amplitude of the contraction increase with 

 increased strength of stimulus, but also the duration of the contraction 

 increases. There is marked persistence of contraction in the stronger 

 reflexes, recalling the " after-discharge " ^ of strong reflexes excited by longer 

 stimuli. An advantage in using tlie single induction shock as a stimulus 

 is that fatigue tends to occur hardly at all. The interval between the 

 successive reflexes in the examples shown was one minute, but even with 

 much shorter intervals no evidence of fatigue was obvious. Care has to be 



^ Proc. Roy. Soc, loc cit. 



2 All the figures read from left lo right ; in all the time record i.s marked in fifths of 

 seconds. 



3 Sherrington, C. S., Journ. of Physiol., loc. cit. ; Integral. Action etc. 



