442 Prof. C.S. Sherrington and Miss 8. C. M. Sowton. [Dee. 30, 
/ 
changing from contraction to inhibition as the stimulation proceeds. Of 
this examples have been already furnished above (fig. 3). The weak reflex 
contractions of the extensor evoked by mild intensities of stimulation, very 
little above threshold value, given by the rotating rheonome, show little and 
sometimes nothing of either of the above forms of decline. Nor is their 
long duration merely simulated by the intervention of after-tonus supporting 
them in the way it supports shortenings of the muscle in virtue of the 
plasticity of the tonic muscle.* This possibility is negatived by the fact 
that on cessation of the stimulus the contraction at once, though gradually, 
subsides (fig. 5). 
II. Apart from intensity and form of the electric stimulus, a further 
condition essential for eliciting extensor contraction-reflexes from 
afferents of the selfsame limb is the absence of “shock” in the preparation. 
These ipsilateral reflex contractions are, in our experience, unobtainable 
in the decapitate preparation. Obtainable in the decerebrate preparation by 
the above-described means when the muscle exhibits good reflex tonus, 
they are poor or inelicitable if the tonus is imperfect. It appears to us that 
conditions which impede the development of the extensor tonus, or set that 
tonus aside, similarly impede or set aside these ipsilateral reflex contractions 
of the extensor. The association thus evident between these reflex con- 
tractions and the reflex tonus, together with the features of the contractions 
as elicited by the rotating rheonome and the resemblance they bear to reflex 
tonus itself, suggests that these contraction reflexes are essentially tonus 
reflexes. The incidence of these reflexes and of the tonus is upon the very 
same muscles of the limb. We think that, especially as elicited by the weak 
galvanic stimuli from the rotating rheonome, these reflex contractions are in 
fact to be regarded as accessions of tonus, the reflex outcome of the electric 
stimulation. 
To regard them as tonus reflexes seems justified further by outstanding 
forms which these reflexes sometimes assume. Fig. 7 exemplifies such a case. 
On applying to ipsilateral popliteal the weak galvanic stimulation through the 
v. Kries rheonome, the knee-extensor began to slowly shorten, its tonic 
length continuing to shorten throughout the 30 seconds during which the 
same unaltered stimulation was in progress. On discontinuing the stimulation 
the muscle remained of the length to which the electrically-induced tonus 
reflex had brought it; this after-maintenance being the result of the plasticity 
of the preparation (“ shortening reaction ”’\.| Highteen seconds later the same 
afferent nerve as that which under the galvanic rheonome stimulus had 
* Sherrington, ‘ Quart. Journ. Exp. Physiol.,’ 1909, vol. 2, p. 109. 
+ Sherrington, ‘Quart. Journ. Exp. Physiol.,’ 1909, vol. 2. 
