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Updated: June 6, 2025
Again, the ordinary supply of blood to a part may be lessened, so that the organ is reduced to a state of inactivity, as occurs in the case of the brain during sleep. We have in the act of blushing a visible example of sudden enlargement of the smaller arteries of the face and neck, called forth by some mental emotion which acts on the vaso-motor center and diminishes its activity.
The more blood passes through the skin, the greater will be the loss of heat by conduction, radiation, and evaporation. Hence, any action of the vaso-motor mechanism which causes dilatation of the cutaneous capillaries, leads to a larger flow of blood through the skin, and will tend to cool the body. Again, the special nerves of perspiration act directly as regulators of temperature.
The effect upon the latter is probably due to the spinal nerve-fibres contained in the plexus, and upon which the ganglionic excitement acts like the galvanism in Schiff's experiment, already described. Direct stimulation of the vaso-motor nerves, alone, as has been said, contracts the blood-vessels. Stimulation of the spinal fibres associated with them exercises the contrary effect.
The Nervous Control of the Blood-vessels. The tone and caliber of the blood-vessels are controlled by certain vaso-motor nerves, which are distributed among the muscular fibers of the walls. If the nerves are stimulated more than usual, the muscular walls contract, and the quantity of the blood flowing through them and the supply to the part are diminished.
Repeated excitement and consecutive paralysis of the vaso-motor nerves, therefore, serve as the most efficient means of draining off the force of the cerebro-spinal nervous system.
Did not his qualifications, his membership, and the record of his writings fill a long half-column in the "Medical Directory," from his first little paper on the "Gouty Diathesis" in 1859 to his exhaustive treatise upon "Affections of the Vaso-Motor System" in 1884?
But galvanism applied to the spinal cord in the neck, causes contraction of blood-vessels. Mechanical irritation of other parts of the spinal cord, on the other hand, causes vaso-motor paralysis and dilatation of blood-vessels.
Vaso-motor Phenomena. In the majority of cases there is an initial rise in the temperature of the part (2° to 3°
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