RESPIRATION 237 



food. Sometimes the rejected food is simply regurgitated after 

 having reached the lower end of the oesophagus, without entering 

 the stomach. The fatal result is usually caused, or at least pre- 

 ceded, by changes of a pneumonic nature in the lungs. The pre- 

 cise significance of the pulmonary lesion is obscure. But it would 

 seem that paralysis of the laryngeal and cesophageal muscles, 

 with the consequent entrance of saliva, food, or foreign bodies, 

 carrying bacteria into the lungs, is responsible to a great extent. 

 And when only a partial palsy of the glottis is produced, by divid- 

 ing the right vagus below the origin of the recurrent laryngeal, 

 and the left as usual in the neck, pneumonia either does not 

 occur or is long delayed. It may be that the tissue of the lungs 

 is rendered particularly susceptible to such insults in consequence 

 of trophic or vascular changes induced by section of the pul- 

 monary and cardiac fibres in the vagi. It may be quite clearly 

 demonstrated, however, in animals which live for some weeks, 

 that, notwithstanding the paralysis of the glottis associated with 

 aphonia, no pulmonary symptoms may be present till a day or 

 two before death. The picture presented in these cases is that 

 of an animal suffering, above all, from alimentary disturbances. 

 The respiration is, to be sure, very different from the normal in 

 frequency, depth, and type, but there is nothing to suggest that 

 the lungs are the seat of any pathological process. Suddenly 

 the picture changes. Pulmonary symptoms obtrude themselves. 

 The physical signs of consolidation of the lungs may be detected, 

 and in a short time the animal is inevitably dead. Occasionally 

 the determining cause of the pulmonary lesion seems to be some 

 external circumstance, as a sudden fall of the air temperature. 

 The idea is exceedingly apt to present itself to the observer that 

 the pneumonia is an accident, an acute intercurrent affection 

 breaking the course of a chronic malnutrition, which in any case 

 must have ended in death. Of course, the vagotomized animal is 

 predisposed to this accident, but there is no definite time after 

 section of the nerves at which it must take place. The vomiting 

 is certainly connected with the paralysis and consequent dilatation 

 of the oesophagus; and by previously making an artificial opening 

 into the stomach, or by a surgical prophylaxis still more heroic, 

 the establishment of a double gastric and cesophageal fistula 

 (p. 374), death may be prevented for many months. Elimination 

 of all the pulmonary fibres of the vagi, by extirpation of one lung, 

 followed after an interval by section of the opposite vagus in the 

 neck, is not fatal in rabbits. This is also in favour of the view 

 that in double vagotomy the stress falls mainly on the diges- 

 tive system. 



Innervation of the Bronchial Muscles. Both constrictor 

 and dilator fibres for the bronchi are contained in the vagus. 



