. The Biological bulletin. Biology; Zoology; Marine biology. TEMPERATURE EFFECTS ON CRAB HEARTS 389 Table I Correlation values and their significances between the difi~erent variables measured in isolated hearts of Cancer magister Correlation Temp range •Pvcnt EMG J» Q V, T 5°-30°C *** (219) *** (199) *** (219) *** (186) *** (186) S'-IO'C *** (186) ** (166) *** (186) *** (153) *** (153) -Pvem 5°-30°C *** (199) *** (199) *** (186) *** (186) S^-IO^C *** (166) *** (166) *** (153)
. The Biological bulletin. Biology; Zoology; Marine biology. TEMPERATURE EFFECTS ON CRAB HEARTS 389 Table I Correlation values and their significances between the difi~erent variables measured in isolated hearts of Cancer magister Correlation Temp range •Pvcnt EMG J» Q V, T 5°-30°C *** (219) *** (199) *** (219) *** (186) *** (186) S'-IO'C *** (186) ** (166) *** (186) *** (153) *** (153) -Pvem 5°-30°C *** (199) *** (199) *** (186) *** (186) S^-IO^C *** (166) *** (166) *** (153) *** (153) EMG 5°-30°C *** (199) *** (170) *** (170) 5°-20°C *** (166) *** (137) *** (137) /h 5°-30°C 5°-20°C * (186) ns (153) *** (186) *** (153) Q 5°-30°C 5°-20°C *** (186) *** (153) EMG, electromyogram amplitude;/h, heart rate; P^^m, ventricular pressure; Q, cardiac output; T, temperature; V^, stroke volume; P < = ***. P < = **, P = ns. Values for cardiac output and stroke volume for the one experiment where flow increased with temperature were not incorporated in these calculations. The number of datapoints is given in brackets. with temperature over the range 4°-12°C {P < ) in both semi-isolated hearts and in intact crabs (Fig. 4). For the semi-isolated hearts, the regression equation was — • r(rin degrees Celsius). Stroke volume of intact animals stabilized at higher temperatures. EMG peak amplitude was measured only in semi-iso- lated hearts. A significant negative relationship (Table I) was found between EMG peak amplitude and tempera- ture. EMG amplitude decreased rapidly with temperature above 20 °C, until it became erratic and of very low am- plitude at 30°C (Fig. 5). The effect of temperature on EMG amplitude was reversible for temperatures up to 30 °C. The decrease of EMG peak amplitude with in- creasing temperatures a
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