On reciprocal innervation of antagonistic muscles.―Eighth note

The following note deals more especially with observations on inhibition occurring in instances of "reciprocal innervation" obtained as a spinal reflex reaction. My view is that inhibition of this kind is part and parcel of the normal reflex process, so that in a reflex it goes on side by side with excitation of other muscles opposed to those which are inhibited. One main consideration which supported the view is the correspondence of the skin-fields whence the reflex contraction of the one set of muscles and the inhibition of the opposed set of muscles can be elicited. So, also, the correspondence of the afferent nerve-trunks, and of the points of surface of the central nervous system whence are elicited the two effects. But to test the view further, I have now attempted to examine in some particulars the conditions attaching to the initiation, and the course run by the two phenomena under comparable circumstances. I. Even in one and the same spinal region the modes of origination, time-relations, etc., of the several elicitable,e. g ., in the dog's hind limb, the "extensor thrust," the "direct-flexion reflex," the "scratch reflex," differ so greatly for each of the types as compared with the others, that in order to compare the inhibition phenomenon with the excitation phenomenon it is important to take both the phenomena from the same type-reflex. The type-reflex I have taken for the purpose has been the "direct-flexion reflex" of the hind limb.