Electro-physiology (1896-98) Electro-physiology electrophysiolog01bied Year: 1896-98 98 ELECTRO-PHYSIOLOGY CHA1>. approximate constancy of steepness in the descending portion. Yet this constancy relates only to a given upper portion of the curve. The final return to equilibrium occurs more and more slowly with decrease of temperature (and contraction residue). There is a marked difference in the effect of cold, and of fatigue, with regard to the time-relations of muscular contraction : on cooling, the descending portion of the curve is as steep as, or steeper than, the ascending portion ;
Electro-physiology (1896-98) Electro-physiology electrophysiolog01bied Year: 1896-98 98 ELECTRO-PHYSIOLOGY CHA1>. approximate constancy of steepness in the descending portion. Yet this constancy relates only to a given upper portion of the curve. The final return to equilibrium occurs more and more slowly with decrease of temperature (and contraction residue). There is a marked difference in the effect of cold, and of fatigue, with regard to the time-relations of muscular contraction : on cooling, the descending portion of the curve is as steep as, or steeper than, the ascending portion ; but in fatigue, which equally prolongs the contraction-process, it is found by all authors to be less steep. A second conspicuous effect, overlooked in earlier researches, is the rise in height of the contractions, visible within a certain range, on cooling. The lift shows an absolute minimum near the freezing-point (of muscle-substance), where no further alteration FIG. 45.—Schematic representation of isotonic curves of contraction at different temperatures. (-5 to + 42i°C.) (J. ) in height can be observed on stimulation, and a relative mini- mum at about 19° C., from which point it rises to the alxu/utr maximum at about 30° C., and the relative maximum at QJ C. The minimum duration of contraction coincides with the absolute maximum of lift, and increases constantly from this point, with falling temperature, until the contraction disappears. The latent period behaves like the period of contraction, increasing con- stantly with falling temperature. We have said that an absolute maximum of twitch was reached at about 30° C.; if the tempera- ture rises beyond this, excitability and height of lift decrease more and more, while the duration of contraction remains approximately equal (Fig. 45, A). At a moderate rate of heating it is possible to show that the excitability of muscle to electrical stimuli disappears almost entirely before the appearance of contraction fro
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