. Electro-physiology. Electrophysiology. 130 ELECTRO-PHYSIOLOGY CHAP. continuous, or summated, contraction (tetanus); there can only lie a series of contractions interrupted by marked pauses. Bow- ditch was the first to determine by excitation of the frog's heart that even where the single induction shocks are separated by intervals of several seconds, the number of the contractions is often less than that of the stimuli. This disproportion between stimulus and contraction is even more striking where the former are working in quick succession, when the muscle of the heart will often fail to re
. Electro-physiology. Electrophysiology. 130 ELECTRO-PHYSIOLOGY CHAP. continuous, or summated, contraction (tetanus); there can only lie a series of contractions interrupted by marked pauses. Bow- ditch was the first to determine by excitation of the frog's heart that even where the single induction shocks are separated by intervals of several seconds, the number of the contractions is often less than that of the stimuli. This disproportion between stimulus and contraction is even more striking where the former are working in quick succession, when the muscle of the heart will often fail to respond to a whole series of excitations (Basch, 5). Under these conditions a new cardiac rhythm, dependent on in-. FIG. 00. — Bulbus aortii- (Frog), tetanising excitation with induction currents. Stiumlation- frequeiu-y, SO per sec. Tuning-fork tracing, £ sec. Tlie ciphers under the figures give in- tensities of tetanising currents. Intensity of coil pushed home = 1000. (Engelmann.) tensity and frequency of the stimulus, is always developed, since, as Engelmann (6) found on tetanising the bulb of the frog's heart with alternating currents, a very low excitation-strength will, after some time, produce a s}'stole by "latent summation," followed perhaps by another, or several. The latent period of the first, and the intervals of the subsequent, contractions, are longer in proportion as the single stimuli are weaker. AYith growing density of the exciting current the duration of the latent period soon becomes minimal, as also the interval between each systole (Fig. GO). Even with the strongest currents Engelmann found no complete relaxation of the bulb after the first contraction; it remained in tetanus at a certain Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Biedermann, W. (Wilhelm), 185
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