OBSERVATIONS ON THE DUAL CONTRACTION OF CRUSTACEAN MUSCLE

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Abstract
The slow and quick types of contraction of skeletal muscle of certain crustacea have been investigated and characteristics of the two types of contraction are described. These contractions are correlated with "twitch" and "Contracture" of vertebrate muscle. By appropriate stimuli, one may excite either type of contraction selectively or may excite both simultaneously. When both types are produced by a single strong stimulus, the slow contraction functions to sustain and continue the tension developed by the quick contraction. Due to the remarkable powers of summation associated with excitation of the slow contraction, it is most easily excited by repetitive stimuli of low intensity. Possibilities of a humoral factor are suggested. On such a slow contraction, quick contractions may be superimposed by sudden increase of frequency or intensity. Thus by appropriate stimuli one may excite either type of contraction selectively or may excite both simultaneously. The function of multiple innervation is discussed briefly.