American journal of physiology . normal, the heartregained its usual rhythm. In tracing B of Fig. 6 we have a similar effect upon the actionof the heart, but in this case it was produced by a lowering ofthe blood pressure. The right half of the tracing shows thenormal rhythm in the early part of the experiment. Later onin the experiment there had been some loss of blood and prob-ably also some loss of vascular tone; a lower blood pressureresulted and the heart showed an arhythmic action. During the Sewall and Donaldson: Journal of physiology, 1880-82, iii, p. 362. Vasomotor Phenomena in the Tu
American journal of physiology . normal, the heartregained its usual rhythm. In tracing B of Fig. 6 we have a similar effect upon the actionof the heart, but in this case it was produced by a lowering ofthe blood pressure. The right half of the tracing shows thenormal rhythm in the early part of the experiment. Later onin the experiment there had been some loss of blood and prob-ably also some loss of vascular tone; a lower blood pressureresulted and the heart showed an arhythmic action. During the Sewall and Donaldson: Journal of physiology, 1880-82, iii, p. 362. Vasomotor Phenomena in the Turtle 249 interval indicated by the dash on the lower line, a stimuluswas apphed to the fibres of the posterior splanchnic. A vaso-constriction followed which increased the blood pressure toapproximately normal and during this period the arhythmicheart action disappeared; but when the stimulus was cut oflfand the blood pressure fell the arhythmia appeared again. Itseems evident from these results that increase in blood pressure,. WSWWifM«« V^/Ajs^f\M^^**^^^ A B Figure 6. A, Record of arhythmic heart action following occlusion of the pulmonaryartery. B, Record of the effect of splanchnic stimulation upon arhythmia. Timeline indicating seconds is also abscissa. such as may be produced by an occlusion of part of the arterialsystem or by vasoconstriction from adrenalin, and lowering ofblood pressure, as produced by hemorrhage or loss of arterialtone, may both be factors in producing an arhythmic heartaction. Discussion. — The experiments outlined in the foregoingpages show that vasoconstriction can be called forth by stimu-lation of the sympathetic fibres supplying the splanchnic result is slower than in mammals, nevertheless in a perfectlyfresh turtle there are often exhibited a delicacy of response anda gradation of action that closely approximate the conditions inthe mammahan mechanism. I have been able with some indi-viduals to obtain a perceptible response, ,
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