. Kirkes' handbook of physiology . motor center, therefore, is capable of pro-ducing rhythmical undulations of blood pressure. Vaso-dilator Nerves. Claude Bernard discovered that the bloodflow was increased through the salivary glands by stimulation of the nerves(the chorda tympani for the submaxillary, and the tympanic branch of theglossopharyngeal for the parotid), thus proving that the arteries have not 218 THE CIRCULATION OF THE BLOOD only vaso-constrictors, but also vaso-dilator nerves. Vaso-dilator nerveshave been described for most parts of the body. In general they are dis-tributed in
. Kirkes' handbook of physiology . motor center, therefore, is capable of pro-ducing rhythmical undulations of blood pressure. Vaso-dilator Nerves. Claude Bernard discovered that the bloodflow was increased through the salivary glands by stimulation of the nerves(the chorda tympani for the submaxillary, and the tympanic branch of theglossopharyngeal for the parotid), thus proving that the arteries have not 218 THE CIRCULATION OF THE BLOOD only vaso-constrictors, but also vaso-dilator nerves. Vaso-dilator nerveshave been described for most parts of the body. In general they are dis-tributed in the same nerve trunks which bear the vaso-constrictors. It is not supposed that the vaso-dilators produce widening of the arteriolesby stimulation to active muscular contraction; in fact the circular arrange-ment of the muscle fibers would seem to exclude such a deduction. It isprobable that there is local inhibition of the tonic contraction of the muscles,thus allowing the mechanical factor of the general blood pressure to dilate. Fig. 207.—Plethysmogram of the Hind Limb of a Cat, Showing Vaso-dilatation upon Stimulatingthe Sciatic Once per Second. To be read from right to left. (Bowditch and Warren.) the vessels. The vaso-dilator nerves are characterized by their responseto slowly developed stimuli, shown by Bowditch and Warren, and by theretention of irritability after degeneration of the constrictors has taken place,see figure 207. Vaso-dilator Centers. No distinct medullary center has yet beenshown to regulate the vaso-dilator nerve activity. Such centers, if theyexist, should be influenced by isolating them from their efferent paths, onthe one hand, or by stimulation by afferent channels, on the other. Theformer method of study has revealed nothing that can be compared to thetonic activity of the constrictor center. Efferent dilator-nerve impulses canbe reflexly produced by sensory stimulation. The isolated lumbar cord ofa dog is capable of reflex vaso-dilator activity,
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