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_ Reversal of the Reflex Effect of an Afferent Nerve by Altering 
3 the Character of the Electrical Stuemulus Applied. 
By C. S. SHERRINGTON, F.R.S., and 8. C. M. SowrTon. 
(From the Physiological Laboratory, University of Liverpool.) 
(Received December 30, 1910,—Read March 2, 1911.) 
_ Stimulation of an afferent limb-nerve in the decerebrate or decapitate 
mammal (cat, dog) gives as its reflex result flexion of that limb; during this 
- flexion the pure extensor muscles of the limb relax under central inhibition. 
In the hind limb this reflex effect is observable in the isolated vasto-crureus, 
the main extensor muscle of the knee ; that muscle if engaged in contraction 
relaxes* when the afferent nerve is stimulated. Its elongation is the sign of the 
central inhibition which takes place. If the reflex stimulation be strong the 
muscle relaxes quickly and greatly ; if the stimulation be weak the relaxation 
1s slower and less ample. These results are easily demonstrable by using as 
a stimulus either faradism or mechanical stimulation such as ligation of the 
central stump of the afferent nerve. 
Usual and uniform as this result is, we find it possible in the decerebrate 
preparation under certain conditions to obtain reflex contraction of vasto- 
crureus as well as reflex inhibition, and to elicit the contraction through the 
same afferent nerves as under other conditions so regularly elicit inhibition. 
The conditions influencing the nature of the reflex result in this respect are 
(1) the strength and (2) the form of the electrical stimulus applied to the 
afferent nerve, and (3) the reflex state obtaining in the preparation at the 
time. 
The reflex preparation used in our observations is the same as that employed by one of 
us previouslyt for the examination of extensor reflexes in the limb. The animal, after 
decerebration under profound chloroform narcosis, has the vasto-crureus muscle of one 
limb isolated by severance of all other nerves than its own in the whole limb and by 
actual resection of the flexors and extensors of the hip. The vasto-crureus thus remains 
the only unparalysed muscle in the limb, and its natural attachments and nerve and 
blood supply are undisturbed. The femur is securely fixed in an appropriate metal 
holder. The preparation Jies supine on a warmed table. A thread attached below the 
knee connects the limb with the myograph lever. The afferent nerve to be stimulated is 
carefully separated for as long a length as possible, and the electrical stimuli applied to it 
are delivered by non-polarisable clay electrodes of the du Bois Reymond pattern, slung 
from the ceiling above. 
* Sherrington, ‘ Roy. Soe. Proc.,’ 1893, vol. 53, p. 407. 
_ + Sherrington, ‘Quart. Journ. Exp. Physiol.,’ 1909, vol. 2, p. 115. 
