The Nervous Control of the Blood Vessels

The investigation of the vasomotor system-really began with the work of Claude Bernard (1851) who, following on the work of his fellow countrymen, demonstrated that section of the cervical sympathetic caused dilatation of the vessels of the ear of the rabbit and that stimula-tion of the peripheral cut end of the nerve caused constriction. In the latter observation Bernard was actually forestalled by Brown-Sequard (1852). Similar conclusions were arrived at by Waller (1853). It is interesting to note that Bernard was most impressed by the increased temperature of the rabbit’s ear and thought that the nerve primarily controlled local heat production. A further observation by Schiff (1856) suggested the existence of vasodilator nerves. He found that if an animal in which the section had been made on one side was exercised, the ear of the healthy side became warmer than that deprived of its vasoconstrictor supply. In 1858 Bernard demonstrated the existence of vasodilator nerves by find-ing an increased blood flow through the submaxillary gland, when the.. chorda tympani is stimulated. He also observed that the venous blood became bright red. Since that time an enormous amount of research has been carried out on the vasomotor system. The mechanisms which control the vessels are by no means so clear-cut as those which control the heart. Two distinct influences constantly affect the blood vessels, the vasoconstrictor and the vasodilator mecha-nisms, which are each partly nervous and partly chemical. The impulses concerned emanate from the central nervous system, especially from the medulla where vasoconstrictor and vasodilator centres have been described, although, as in the case of the cardiac centres, these may really be the apices of reflex arcs. It might at first sight be reasonable to imagine that the vasoconstrictor fibres correspond to the sympathetic fibres which accelerate the heart and the vasodilator fibres to the vagus which slows the heart. This is, however, not true as a general state-ment, although it may be true of certain blood vessels. So far as present