Effects of lesion qf the yogi upon the se c re t io n of mucus front the inner surface of the stomach and intestines.—Sir B. Brodie relates from experiments in which animals were poi soned by arsenic where the usual watery and rnucous secretions were not poured out from the mucous surface of the stomach and intestines, though it presented the inflammation usual in such cases.* We have carefully repeated these experiments, and obtained different results. The quantity of watery and mucous secretions was nearly the same in ani mals after the vag,i had been divided, as in animals upon which this operation had not been performed:1- These experiments upon the effects of lesion of the vagi upon the dif ferent secretions poured out from the inner sur face of the digestive canal, though they do not prove that the function of secretion is indepen dent of the nervous system, seeing that nume rous filaments of the sympathetic nerve are also distributed there, are yet sufficient to neutralize the evidence drawn from the effects of lesion of the vagi upon these secretions adduced by those who maintain that secretion is dependent upon the nervous system.
Effects of lesiva, of the yogi upon the rapidity of absolption tom the inner sinface of the stomach.—It has been stated by Dupuyt and Brachet, that the most active poisons in troduced into the stomach after division of the vagi in much lager quantities than usual, pro duce their effects much more slowly. On the other hand Miiller mentions that in thirty ex periments on Mammalia perforrned under his direction by M. Wernscheidt, " not the least difference could be perceived in the action of narcotic poisons introduced into the stomach, whether the nervus vagus had been divided on both sides or not, provided the animals were of the same species and size."§ We have Made several cornparative experiments on this point,Il and obtained results which agreed nearly with those mentioned by Muller.
The following short summary contains the principal conclusions founded upon the facts and observations above detailed, at which we have arrived regarding the functions of the nervus vagus.
1. Though the trunk of the nervus vagus at its attachment to the encephalon principally consists of sensiferous and incident filaments, it yet contains a few motor filaments. The motor filainents contained in some of the branches of the vagus chiefly come from the spinal accessory.
2. The filaments of the auricular branch of the vagus are sensiferous and incident.
2. The pharyngeal branches of the vagus are principally if not entirely motor, and move the muscles of the pharynx and soft palate in obedience to certain impressions rnade upon the incident filaments of the glosso-pharyngeal and fifth pair of nerves distributed upon the mucous surface of these organs.
4. The superior laryngeal branch is chiefly composed of sensiferous and incident filaments which are abundantly distributed upon the muco,us surface of the larynx, and much more sparingly upon the inner surfa.ce of the lower part of the pharynx. The few motor filaments contained in the superior laryngeal are dis tributed in, and move the crico-thyroid muscle. When the superior laryngeal branches are divided or tied, every excitation of the inner surface of the larynx fails to excite sensation, or any reflex and muscular movement, and the two crico-thyroid muscles are paralysed.
5. The olftrior laryngeal or recurrent branch is mmified in, and regulates the move ments of all the muscles attached to the aryte noid cartilages, viz. the crico-arytenoideus pot ticus and lateralis, the thyro-arytenoideus, and the arytenoidei. The inferior laryngeal also furnish the sensiferous filaments to the upper. part of the trachea, a few to the mucous surface of.the larynx, and still fewer to the pharynx. The sensiferous filaments of the inferior laryn geal are, however, few in number and do not impart much sensibility to the parts in which they are distributed, presenting a striking con trast in this respect to the superior laryngeal. When the inferior laryngeal is cut or tied, the muscles attached to the arytenoid cartilages are no longer moved voluntarily as in speech, or involuntarily as in the muscular movements of respiration ; and the arytenoid cartilages may be mechanically carried inwards by the cur rents of air rushing into the lungs, so as to shut up the superior aperture of the larynx and pro duce suffocation. When any excitation is applied to the inner surface of thearynx in the healthy state, this does not produce the con traction of the muscles which approximate the arytenoid cartilages by acting directly upon them through the mucous membrane ; but this muscular contraction is effected indirectly and by a reflex action, in the performance of which the superior laryngeal acts as the incident or afferent nerve, and the inferior laryngeal as the motor or efferent nerve. It is also probable that these filaments of the inferior laryngeal distributed in the muscular fibres of the trachea are motor. The inferior laryngeal branch is the principal nerve of phonation, and when para lysed the voice becomes very faint. The effects of the paralysis of the superior laryngeal upon the voice are much less marked and are much more doubtful.