REFLEX EFFECTS OF STIMULATION OF THE VAGUS. 613 



they also cause vomiting. For the effect of the vagus upon the movements of the 

 intestine (see 161). According to some observers, stimulation of the vagus is 

 followed by movement of the large as well as of the small intestine {Stilling, 

 Kupffer, C. Ludwig, Remah). Stimulation of the peripheral end of the vagus causes 

 contraction of the smooth muscular fibres in the capsule and trabecular of the spleen 

 (in the rabbit and dog, 103). Stimulation of the vagus at the cardia causes in- 

 crease in the secretion of urine with dilatation of the renal vessels, while the blood of 

 the renal vein becomes more arterial (CI. Bernard). According to Rossbach and 

 Quellhorst, a few vaso-motor fibres are supplied by the vagus to the abdominal 

 organs, whilst the greatest number comes from the splanchnic. 



12. Eeflex Effects. The vagus and its branches contain fibres, some of which 

 have been referred to already, which act reflexly (afferent) upon certain nervous 



(a) On the vaso-motor centre there act {a) pressor fibres (especially in both laryngeal nerves), 

 whose stimulation is followed by a reflex contraction of the arterial blood-channels, and thus 

 cause a rise of the blood-pressure ; (#) depressor fibres (in the depressor or the vagus itself), 

 which have exactly an opposite effect. (This subject is specially referred to under the head of 

 the Vaso-motor nerve-centre, 371.) 



(6) On the respiratory centre there act (a) fibres (pulmonary branches) whose stimulation is 

 followed by acceleration of the respiration ; and (j8) inhibitory fibres (in both laryngeals), whose 

 stimulation is followed by slowing or arrest of the respiration. (See Respiratory centre, 368.) 



(c) On the cardio-inhibitory system. [When the central end of one vagus is stimulated, 

 provided the other vagus is intact, the heart may be arrested reflexly in the diastolic phase.] 

 Mayer and Pribram observed that sudden distension of the stomach caused slowing and even 

 arrest of the heart, while, at Jhe same time, there was contraction of the arteries of the medulla 

 oblongata and increase of the blood-pressure. 



(d) On the vomiting centre. This centre may be affected by stimulation of the central end 

 of the vagus, and, as already mentioned, by stimulation of manv afferent fibres in the vagus 

 ( 158). 



(e) On the pancreatic secretion. Stimulation of the central end of the vagus is followed by 

 arrest of this secretion (171). 



(/) According to CI. Bernard, there are fibres present in the pulmonary nerves, which, when 

 they are stimulated, increase reflexly the formation of sugar in the liver, perhaps through the 

 hepatic branches of the vagus. 



Unequal Excitability. The various branches of the vagus are not all endowed with the same 

 degree of excitability. If the peripheral end of the vagus be stimulated, first of all with a weak 

 stimulus, the laryngeal muscles are first affected, and afterwards the heart is slowed (Ruther- 

 ford). If the central end be stimulated with feeble stimuli, the " excito-respiratory " fibres are 

 exhausted before the " inhibito-respiratory " (Burkart), According to Steiner, the variovs 

 fibres are so arranged in the vagus that the afferent fibres lie in the outer, and the efferent in 

 the inner, half of the trunk, in the cervical region. 



Pathological. Stimulation or paralysis in the area of the vagus must necessarily present a 

 very different picture according as the affection is referred to the whole trunk or only to some 

 of its branches, or whether the affection is unilateral or bilateral. Paralysis of the pharynx 

 and oesophagus, which is usually of central or intracranial origin, interferes with or abolishes 

 deglutition, so that when the oesophagus becomes filled with food there is difficulty of breathing, 

 and the food may even pass into the nasal cavities. A peculiar sonorous gurgling is occasionally 

 heard in the relaxed canal (deglutatio sonora). In incomplete paralysis, the act of deglutition 

 is delayed and rendered more difficult, while large masses are swallowed more easily than small 

 ones. Increased contraction and spasmodic stricture of the oesophagus are referred to under the 

 phenomena of general nervous excitability ( 186). 



Spasm of the laryngeal muscles causes spasmodic closure of the glottis (Spasmus glottidis). 

 This condition is most apt to occur in children, and takes place in paroxysms, with symptoms 

 of dyspnoea and crowing inspiration ; if the case be very severe, there may be muscular con- 

 tractions (of the eye, jaw, digits, &c). The symptoms are very probably due to the reflex 

 spasms which may be discharged from the sensory nerves of several areas (teeth, intestine, skin). 

 The impulse is conducted along the sensory nerves proceeding from these areas to the medulla 

 oblongata, where it causes the discharge of the reflex mechanism which produces the above- 

 mentioned results. There may be spasm of the dilators of the glottis and other laryngeal 

 muscles (Frantzel). 



Stimulation of the sensory nerves of the larynx, as is well known, produces coughing. If 

 the stimulation be very intense, as in whooping-cough, the fibres lying in the laryngeal nerves, 

 which inhibit the respiratory centre, may also be stimulated ; the number of respirations is 



