Physiology and biochemistry in modern medicine . re apart from this effect remains unchanged. With thelatter drug (alcohol), on the other hand, the reflex response entirely THE CONTROL OP THE CIRCULATION 239 disappears, although it immediately reappears when the alcohol effecl has passed off, and there is no evidence of a change in tone. The tonicand the reflex mechanisms of the vasomotor center can not therefore be identical. At the present stage of our knowledge, it is only possible for us tostudy the effect of stimulation of pressor and depressor fibers on thevasoreflex center. Such filters
Physiology and biochemistry in modern medicine . re apart from this effect remains unchanged. With thelatter drug (alcohol), on the other hand, the reflex response entirely THE CONTROL OP THE CIRCULATION 239 disappears, although it immediately reappears when the alcohol effecl has passed off, and there is no evidence of a change in tone. The tonicand the reflex mechanisms of the vasomotor center can not therefore be identical. At the present stage of our knowledge, it is only possible for us tostudy the effect of stimulation of pressor and depressor fibers on thevasoreflex center. Such filters are contained in practically every sen-sory nerve of the body, and it would appear that a fairly equal mixtureof both kinds of fiber exists in most of these nerves. Pressor and Depressor Impulses.—Depressor impulses are alone presentin the cardiac depressor nerve. Sometimes as in the rabbit, this existsas an independent nerve trunk, originating by two branches, one fromthe superior laryngeal, the other from the vagus, and descending close to. Fig. 73.—Fall of blood pressure from excitation of the depressor nerve. The drum wasstopped in the middle of the curve and the excitation maintained for seventeen minutes. The lineof zero pressure should be 30 mm. lower than here shown. (From Bayliss.) the vagus trunk, to end around the arch of the aorta. In other animalsthe depressor is bound up with the vagus trunk from which it can some-times be separated by careful dissection. The first prerequisite in inves-tigating the cause of the changes produced by stimulation of these nervesis the elimination of any chance of an alteration in heartbeat as a resultof simultaneous stimulation of afferent vagus fibers. This may be doneeither by cutting both vagi or by administering atropine. Stimulation of the central end of the cardiac depressor nerve in suchan animal causes an immediate fall in blood pressure, accompanied by anincrease in volume which can be demonstrated either in the hind li
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