STUDIES IN THE REFLEXES OF THE GUINEA‐PIG. VI.: ON THE RELATION BETWEEN MAINTAINED CONTRACTION AND RHYTHMIC DISCONTINUOUS INHIBITION

Abstract

1. Tracings obtained from the isolated quadriceps extensor cruris of the scratching movements which occur during ether anæsthesia in the guinea‐pig shew that there are present in the single muscle the phenomena already described in the case of the movements of the intact hind limb under the same circumstances.2. In the composition of the scratching movements there are two factors —the factor of maintained contraction and the factor of rhythmically discontinuous inhibition.3. The maintained contraction is evidenced as flexion. It may be present alone.4. The factor of rhythmically discontinuous inhibition is evidenced as inhibition of the maintained flexion. When present, it determines the characteristic “clonic beats” of the scratch.5. That the “beats” are determined by rhythmic inhibition of a maintained flexion is demonstrated by tracings in which the maintained flexion is at first present alone, but is then complicated by the “clonus.” In these cases the “beats” are produced by relaxations and restitutions of the maintained flexion. The level of the plateau of maintained flexion in the tracings is not overshot.6. The “notched” appearance in some of the tracings of the scratching phases is to be explained by the occasional continuous inhibition of the maintained flexion—in place of the more usual rhythmically discontinuous inhibition.7. The isolation of the muscles for the purposes of recording depresses the scratch—as Sherrington has already observed in the cat. This depression falls more heavily upon the factor of rhythmically discontinuous inhibition. A small dose of strychnine seems to increase the likelihood that the scratching movements will appear. Even then the “clonus” is rarely present.8. The extent of the contraction of the quadriceps extensor cruris in the active scratching phases of the phenomenon varies with the state of the depth of narcosis. It diminishes in successive phases with increasing depth of narcosis, and it increases with diminishing depth of narcosis.9. The extent of the relaxation of the quadriceps extensor cruris also varies under the same circumstances as the variation of the contraction. Complete relaxation of the muscle is not obtained except under the deepest narcosis. There is therefore a certain amount of “residual contraction” of the muscle during the interphases of the phenomenon. This amount of contraction diminishes with increasing depth of narcosis, and increases with decreasing depth of narcosis. It is possibly nearly related to a true tonus in the muscle.