Dr. Isaac Ott, an American physiologist of distinction, states in a description of certain vivisections made by him:
"IT IS A WELL-KNOWN FACT THAT IRRITATION OF A SENSORY NERVE causes an excitation of the vasomotor centre, WHICH IS INDEXED BY A RISE OF PRESSURE…. As indirect irritation ALWAYS PRODUCES A RISE OF PRESSURE, the sensory nerves and the conductors of their impressions up to the (spinal) cord are not paralyzed."[2]
[2] Ott, "On Physiological Action of Thebain," pp. 11-12.
Dr. Leonard Hill, in an article contributed to Schafer's "Textbook of
Physiology" upon the circulation of the blood, says:
"Arterial pressure is affected reflexly BY STIMULATION OF ANY SENSORY NERVE IN THE BODY…. The usual result of stimulating a sensory nerve is A REFLEX RISE OF ARTERIAL PRESSURE."[3]
[3] Schafer's "Textbook of Physiology," vol. ii., pp. 166-167.
The writer goes on to explain that when the tone of the system in weakened "after prolonged experiment OR DURING THE ADMINISTRATION OF CHLOROFORM AND CHLORAL," then a fall of pressure may occur.
This phenomenon was known to physiologists many years ago. For instance, Dr. J. C. Dalton, professor of physiology at the College of Physicians and Surgeons, in his well-known textbook on physiology, says that the most frequent instance of reflex constriction of arteries is that "which follows irritation of the central extremity of a sensitive nerve."
"This effect has been observed by many experimenters, and is regarded as nearly invariable. Galvanization of the central extremity of the sciatic nerve causes general constriction of the bloodvessels throughout other parts of the body, INDICATED BY INCREASED ARTERIAL PRESSURE. A similar result is produced by the irritation of … other sensitive nerves, or nerve roots."[1]
[1] Dalton's "Physiology," pp. 507-508.