270 Prof. C. 8. Sherrington. [Apr. 175 
extensive is characteristic for it. Examined by the above preparation the 
skin-field whence the excitation (contraction) is elicitable and that whence the 
inhibition is elicitable has proved in my observations to be one and the same. 
Thus: stigmatic unipolar faradisation of a point in the skin of a right pedal digit 
provokes in the homonymous limb contraction of the flexors of the knee, and 
similar stimulation of the corresponding left digit provokes in its own limb 
inhibition of the extensors of the knee. Again, similar stimulation of the 
skin of the fore-foot (in my experience that of the crossed fore-foot acts more 
readily than that of the homonymous) induces excitation (contraction) of the 
flexors of the crossed knee; and the corresponding skin-region of the opposite 
fore-limb induces inhibition (relaxation) of the extensors of knee contra- 
lateral to it. | 
(8) Turning to stimuli other than electrical it is not, as I have pointed out, 
every form of stimulus that, when applied within the skin-field appropriate 
for the “ direct-flexion reflex,” can excite it. The kinds of skin-stimuli which 
excite it are those which may be termed “ nocuous,’* eg., a prick, strong 
squeeze, harmful heat (the heat-beam), chemical agents. Touches, innocuous 
pressures, rubbing, etc., though effective for various reflexes, eg., for the 
“extensor thrust,” “scratch reflex,” “ pinna reflex,” etc., do not in my experi- 
ence excite this reflex. The stimuli which do excite it, for instance, from the 
planta, excite, when applied on the side where the flexor muscles alone remain 
intact, contraction of those muscles, and when applied correspondingly on 
the opposite side, where the extensors alone remain intact, inhibit them 
(relaxation). 
(y) The nerve-twig, similar to that which under faradisation on the 
“flexors” side excites the flexors (contraction) when faradised on the 
“extensors” side inhibits the extensors (relaxation). This comparison has 
been made not only with skin-nerves, but with muscular nerves, notably with 
the nerves of the hamstring muscles and of the gastrocnemius. 
(6) The “ flexion reflex,” although it exhibits well the potency of summation 
of successive stimuli as a factor in its initiation, differs in my experience from 
various other reflexes,} e.g., “extensor thrust,” “scratch reflex,” “pinna reflex,” 
in being elicitable fairly easily by a single induction shock. The shock may 
be applied either to the skin in the receptive skin-field of the reflex or to an 
appropriate afferent nerve either cutaneous or muscular. When this is done 
in the prepared limbs the single induction shock applied on the “flexors ” 
side excites a brief reflex contraction of those muscles, correspondingly applied 
on the “ extensors” side it provokes a brief reflex inhibition of those muscles. 
* Sherrington, ‘ Journ. of Physiol.,’ vol. 30, p. 39, 1903. 
+ Cf. Stirling, ‘ Arbeiten a. d. Physiol. Anstalt z. Leipzig,’ 1874. 
