. Electro-physiology. Electrophysiology. 4ft 118 ELECTRO-PHYSIOLOGY CHAP. it becomes intelligible that under certain conditions the height of a summated twitch may far surpass that of its two components. It was shown above that the magnitude of interval between each pair of stimuli must not exceed a certain limit, if the bene- ficial effect of the preceding stimulus is to be observed upon its successor, and it is intelligible that under some conditions tetanus may lie set up in the muscle, in consequence of a rapid succession •of weak stimuli, although these in themselves would produce no visi
. Electro-physiology. Electrophysiology. 4ft 118 ELECTRO-PHYSIOLOGY CHAP. it becomes intelligible that under certain conditions the height of a summated twitch may far surpass that of its two components. It was shown above that the magnitude of interval between each pair of stimuli must not exceed a certain limit, if the bene- ficial effect of the preceding stimulus is to be observed upon its successor, and it is intelligible that under some conditions tetanus may lie set up in the muscle, in consequence of a rapid succession •of weak stimuli, although these in themselves would produce no visible change of form in the muscle. The intensity and frequency of stimulation necessary to produce such a summation (Richet's addition l<tt<'nt<'} must of course depend upon the nature of the muscle. As a general rule, sluggishly reacting muscle is more predisposed to summation of stimuli than quick muscle,. FIG. 50.—A, Simple twitch (muscle of Crab); ,4-, summated twitch, from two closely approximated stimuli of the same magnitude as A. (Richet.) which tallies with the rapid expiration of all phenomena of excitation in the latter, since the persistence of any kind of change in the muscle-substance resulting from a stimulus is the necessary condition of a subsequent heightening of excitability. The comparatively sluggish striated muscle of the heart may be indicated as peculiarly suited to summation effects in the above sense. Basch (5) showed that subliminal, single, electrical stimuli, inadequate in themselves to produce any contraction, will gradually (addition latcnte) increase the excitability of the heart- muscle (frog) if led into it at short intervals, until finally con- tractions will be discharged. Engelmann (G) made similar obser- vations on the bulbus aortas of the frog's heart, which also exhibits unmistakable effects of summation when rhythmically excited; the most obvious instances, however, are in smooth muscle. Here. Please note that these images ar
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