5. The (esophageal branches of the vagus are partly afferent and partly efferent nerves. In some animals, as in the rabbit, the section of the vagi in the neck is folloWed by the sus pension of the niovements of the cesophagus during deglutition, and the food is no longer conveyed along it in the usual manner. This lesion of the vagi does not produce these effects by destroying the contractility of the muscular fibres of the cesophagus, but by breaking the continuity of the nervous circle necessary for the accomplishment of all reflex movements. In some other animals, as in the dog, the food is still propelled along the cesophagus after section of the vagi, so that it is probable that in these animals the muscular fibres of the ceso phagus are also called into contraction by direct excitation.
6. The cardiac branches of the vagus have no direct effect in maintaining the movements of the heart. Though the movements of the heart may be materially influenced by causes acting through the vagus, yet mental emotions and injuries of the central org-ans of the nervous systetn affect the heart's action through the sympathetic after the vagi and recurrents have been divided in the neck.
7. The pulmonary branches of the vagus con sist chiefly of incident filaments and convey impressions, capable of producing respiratory muscular movements, made on the inner sur face of the lungs to the medulla oblongata.
When the vagi are cut or tied in the neck the respirations instantly fall in frequency, and are reduced to about one half their former number. The existence of motor filaments in these branches has not yet been satisfactorily esta blished.
8. Though excitation of the nervus vagus in the neck causes muscular contractions of the stomach, yet the muscular movements of the stomach are not entirely dependent upon the gastric branches of the vagus, and the stomach may still propel the chyme into the duodenum after the vagi aud recurrents have been divided. Lesion of the gastric branches of the vagus does not necessarily arrest the secretion of the usual fluids poured out into the interior of the sto mach, though these are generally changed to a considerable extent both in quantity and quality by causes acting through the nervous system. The mpidity of the absorption of poisonous substances from the inner surface of the sto mach is not perceptibly diminished by the division of the vagi.
9. Division or ligature of the vagi in the neck is almost always fatal. The cause of death, in by far the greater number of cases, is congestion of the lungs with blood induced by the diminished frequency of the respiratory muscular movements. In a few cases the ani mal dies of inanition from derangement of the functions of the stomach.* (John Reid.)