The following phenomena were observed on strips of the ventricular muscle of the turtle, suspended in saline solution.
(1)
Increase of temperature shortens the dormant (prerhythmic) period; quickens the rhythm, and shortens the endurance. These phenomena occur under all the conditions to be discussed; but unler unfavorable conditions, the higher temperatures show less of the beneficial and more of the detrimental effects, so that with these these is a “break” in the temperature curve.
(2)
Aeration of the solution shortens the dormancy, diminishes irregularities in the curves, and prolongs the endurance.
(3)
Oxygen deficiency acts in the opposite direction. With moderately high temperatures, the muscle often fails to initiate contractions in non-aerated isotonic (0.7%) NaCI. Such failure is rare if the solution is aerated, or if the plasma concentration of CaCl
2 is added.
(4)
Calcium Chloride: The addition of the plasma con-centration (0.025%) of calcium chloride to isotonic NaC1 shortens the dormant period, quickens the rhythm, and prolongs the endurance, notwithstanding the greater work that is performed by the muscle. It counteracts the deleterious effects of the heat and therefore permits the full development of the stimulant effects of higher temperatures.
(5)
Potassium Chloride: The plasma concentration of ROl (0.03%) generally renders the ventricle non-rhythmic. With 0.015% Ed, the dormant period is prolonged; the rate is slower and cannot follow the quickening effects of higher temperatures; the endurance is not materially altered.
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