EXPERIMENTS ON THE CERVICAL VAGUS AND SYMPATHETIC

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Abstract
1. No evidence could be obtained of functional regeneration of the peripheral vagus as long after section of the nerve as two years and fifty days (in the cat).2. The fatal result which follows double vagotomy, and which occurs within three days after section of the second vagus, no matter how long previously the first has been cut, is due not to pneumonia but to slow asphyxia caused by obstruction at the glottis from paralysis of the laryngeal muscles. If precautions are taken to obviate this, animals survive the double operation indefinitely, and show no abnormal symptoms except a certain difficulty in swallowing, with sometimes a tendency to vomit, and an increased rapidity of pulse‐rate.3. Although slowing and depression of the respiratory movements often result from section of both vagi, the phenomenon is not constant, and, if the trachea is previously opened, it may not occur at all. Even if under these circumstances it does occur it is not persistent, but disappears within a few hours, sometimes within a few minutes, of section of the second nerve.4. Especially when a prolonged period has elapsed since the section of the first vagus, the “slow, deep inspirations” which form the classical picture of the effect of double vagotomy are not observed, provided tracheotomy has been performed. Without this precaution the obstruction to inspiration caused by the falling together of the thyro‐arytenoid ligaments tends to produce slow and deep dyspneic respirations and, ultimately, asphyxia.5. In the dog and cat when the sympathetic nerves are cut in the neck—either along with the vagus or separately—the resulting symptoms in the eye and in the vessels of the ear have been found to persist as long as the animal was kept alive—one dog for nearly two years, one cat for more than two years,—although becoming generally less manifest as time went on. If the sympathetic of the opposite side is now severed, provided a certain interval of time (the exact period of which has not yet been determined, but which probably exceeds eight days) has elapsed since the first operation, the symptoms, which are at once very pronounced on the side of the second section, may disappear on the side of the first section and may even be replaced by a “swing” in the opposite direction; i.e. the pupil becomes abnormally dilated, the eye abnormally prominent, the membrana nictitans may entirely disappear, and the blood‐vessels of the ear become contracted so that that ear is cold to the feel. These “reversal” conditions tend gradually to pass off; but as long as the animals have been kept alive there remains a decided difference on the two sides, the signs of section being always more obvious upon the side last operated on.6. In rabbits the effects of section of one cervical sympathetic (or extirpation of one superior ganglion) and of successive section of both nerves (or extirpation of both ganglia) are more variable, being only in some individuals similar to those described in the cat and dog. In other individuals the effects are fugitive or may even pass unnoticed, if present at all.7. Certain effects of section of the cervical sympathetic in producing activity of the salivary and lacrimal glands are noticed and briefly discussed.This work has been assisted by grants of money from the Carnegie Trust for the Universities of Scotland, and from the Earl of Moray Endowment for the Promotion of Original Research in the University of Edinburgh.I desire to thank Dr May Walker, Lecturer on Experimental Physiology in the University, for aiding me in a number of the later experiments recorded in this paper.A preliminary account of experiments on section of both vagi has been published in the Comptes rendus de la Société de Biologie, 1918, lxxxi. 1135; and of others, dealing both with vagal and sympathetic section, in the Proceedings of the Physiological Society, 7th June 1919, and in Compt. rend. de la Soc. de Biol., 1919, lxxxii. 816.

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