7 io 



VAGUS NERVE. 



tion of the intestinal nerves. According to some observers, irritation 

 of the vagus causes movements in the small as well as in the large 

 intestine. Irritation of the peripheral stump of the vagus causes in the 

 spleen contraction of the unstriped muscular fibers in the capsule and 

 in the trabeculae (in the dog and the rabbit). With respect to the kid- 

 neys, irritation of the vagus at the cardia causes increased secretion of 

 urine, with dilatation of the renal vessels and redness of the blood in 

 the renal veins. In dogs and rabbits a number of vasomotor fibers are 

 said to be supplied to the abdominal viscera by the vagus, while the 

 overwhelming majority are derived from the splanchnic. 



The trunk and the branches of the vagus contain also fibers (in 

 part already mentioned), irritation of which acts in a centripetal direction 

 upon certain nervous stuctures: 



(a) The vasomotor center is affected through (n) pressor fibers (especially 

 in the two laryngeal nerves) , irritation of which causes reflex contraction of -the 

 arteries and thus increase in blood-pressure ; (/?) depressor fibers (in the depressor 

 nerve or in the vagus itself), which exert a contrary effect. This subject is dis- 

 cussed in connection with the vasomotor center. 



(6) The respiratory center is affected through (</) accelerator fibers (pulmonary 

 branches), irritation of which accelerates the respiration; and (/?) inhibitory 

 fibers (in the two laryngeal branches), irritation of which inhibits respiration. 

 This subject is discussed in connection with the respiratory center. 



(c) The cardio-inhibitory system is influenced through fibers in the trunk of 

 the vagus, irritation of which acts on the center in a centripetal direction and 

 places the heart in a condition of diastolic rest. Irritation of the central stump 

 of the vagus, therefore, causes arrest of the heart. In conformity with these facts 

 is the observation of Mayer and Pribram that sudden dilatation of the stomach 

 causes slowing and even arrest of the heart, the arteries of the medulla oblongata 

 contracting at the same time with increase in blood-pressure. 



(d) The vomiting center is excited by irritation of the central stump of the 

 vagus and of a number of centripetal fibers of the vagus. 



(e) The secretion of the pancreas is influenced by irritation of the central stump 

 of the vagus, the secretion being arrested in this way; therefore, probably through 

 the intermediation of certain pancreatic nerves. 



(/) According to Claude Bernard the pulmonary branches contain fibers, 

 irritation of which causes reflex increase in the formation of sugar in the liver, 

 perhaps through the intermediation of the hepatic branches of the vagus; for 

 after section of both vagi the formation of glycogen in the liver ceases. Con- 

 versely, irritation of the peripheral stump of the vagus causes an increase in the 

 formation of sugar in the liver. 



The various branches and paths of the vagus possess an unequal degree of 

 irritability. If irritation, at first feeble, be applied in a centrifugal direction, the 

 muscles of the larynx move first, then the heart-beat is slowed. If the central 

 stump is stimulated the excito-respiratory fibers become exhausted, even on feeble 

 irritation, and only later the inhibito-respiratory fibers. According to Steiner, 

 the various fibers are so arranged in the vagus of the rabbit that the centripetal 

 are situated in the outer and the centrifugal in the inner half of the cervical trunk. 



Pathological. Irritation or paralysis in the distribution of the vagus will 

 present a varying clinical picture accordingly as the lesion involves the entire 

 trunk or only individual branches, and accordingly, also, as the affection is unilateral 

 or bilateral. Paralysis of the pharynx and the esophagus, which is generally of 

 central or at least intracranial origin, renders difficult or abolishes movements of 

 deglutition, so that stagnation in the esophagus, entrance of foreign bodies into 

 the larynx, dyspnea, and the passage of food into the nares are observed. In drink- 

 ing, a rumbling murmur is at times audible in the relaxed tube (deglutatio sonora) . 

 When the paralysis is incomplete, the act of swallowing is only delayed and ren- 

 dered difficult, and large masses of food are most -readily swallowed. Increased 

 contraction, even spasmodic constriction, is observed in association with the symp- 

 toms of general nervous irritability. 



Spasm of the muscles of the larynx causes especially spasmodic closure of the 

 glottis, so-called spasm of the glottis. The latter is peculiar to childhood, and 

 occurs paroxysmally with dyspnea, tight, whistling inspiration, with which twitch- 

 ing of the muscles of the eyes, the jaw, the fingers, the toes, etc., may be associated. 



