556 Prof. C. 8S. Sherrington. On Reciprocal [Aug. 10, 
permanence a new tonic length shorter than that which it had previously. 
This reaction may for brevity be termed the “shortening reaction.” 
This reaction appears on grounds very similar to those advanced in regard 
to the “lengthening reaction” to be reflex, and to be traceable to reflex ares 
arising in the muscle itself. (1) The “shortening reaction” of vasto-crureus 
is not obtained after severance of those afferent spinal roots through which 
pass the afferent nerve-fibres proceeding from the vasto-crureus muscle. 
Fig. 3a. 
Passive manipulation then fails altogether to elicit it. Where the afferent 
spinal roots of one vasto-crureus had been cut 20 to 80 days prior to comparing 
the reflexes from thetwo vasto-crurei in the decerebrate animal, the reflex 
contractions exhibited by the vasto-crureus with afferent fibres cut (fig. 2B, 
fig. 38, fig. 48) showed nothing of the long maintained tonic after-contraction 
exhibited by the fellow muscle whose afferent fibres still remained intact 
(fig. 24, fig. 3a, fig. 4a). Reflex contraction of the muscle with its afferent 
nerve-fibres cut is, therefore, when evoked by slowly repeated stimuli, more 
clonic than is that of the muscle with its afferents intact (fig. 5, A and B). 
