708 VAGUS NERVE. 



The function of the pulmonary branches of the vagus is a varied 

 one : ( i ) They supply the motor branches for the unstriated muscles of 

 the entire bronchial tree. (2) They supply the sensory fibers (exciting 

 cough) to the entire bronchial tree and the lungs. (3) They supply, 

 in smaller part, vasomotor nerves to the pulmonary vessels, although 

 these are in largest part, if not wholly, derived from the anastomosis 

 with the sympathetic (in animals from the superior thoracic ganglion). 

 (4) They contain, in the ape situated in the posterior portion of the 

 trunk of the vagus itself, centripetal fibers passing from the parenchyma 

 of the lungs to the medulla oblongata, irritation of which stimulates 

 the respiratory center. Division of both vagi is, accordingly, followed 

 by marked reduction in the number of respirations, which at the same 

 time are deepened, so that the animals for a time exchange the normal 

 volume of air containing normal amounts of oxygen and carbon dioxid. 

 Irritation of the central stumps of the vagi causes acceleration 

 of respiration. This labored and embarrassed breathing is explained 

 as due to elimination of these reflex-stimulating fibers, which main- 

 tain the normal easy play of reflex breathing. After division of 

 the nerves, the stimulation of the respiratory movements must take 

 place in the medulla oblongata itself. (5) They contain centripetal 

 fibers, irritation of which has a depressant effect upon the vasomotor 

 center, as shown by fall of the blood-pressure on forced expiratory 

 pressure. (6) Also fibers, irritation of which has an inhibitory influence 

 upon the cardiac inhibitory fibers of the vagus, thus accelerating 

 the pulse. Simultaneous irritation of the last two sets of fibers men- 

 tioned is capable of altering the rhythm of the pulse. 



Carbon dioxid, as well as the vapors of ammonia and chloroform, introduced 

 into the air-passages, cause (from the mucous membrane of the large bronchi) 

 inspiration, while, acting upon the entrance to the respiratory tract situated above 

 the trachea, they cause reflex expiration. 



Pneumonia after section of both vagi has attracted the interest of investigators 

 since the time of Valsalva (died 1723), Morgagni (1740) and Legallois (1812). 

 In explanation of this condition the following facts are to be taken into con- 

 sideration: (a) In the first place, section of both vagi is attended by loss of 

 the motility of the larynx, as well as of the sensibility of the larynx (if the section 

 has been made above the origin of the superior laryngeal nerve), the trachea, 

 the bronchi, and the lungs. Therefore, the larynx fails to close during the act of 

 swallowing, and reflex closure of the larynx when foreign bodies threaten to enter 

 (fluids in the mouth, particles of food, irritating gases) does not take place, and 

 reflex cough for the expulsion of substances that have entered is suppressed. 

 Thus, foreign bodies enter the lung without hindrance, and all the more readily 

 as the associated paralysis of the esophagus permits the food to remain lodged 

 in this tube for a time, and thus readily enter the larynx. That herein resides an 

 essential exciting factor for the inflammatory process Traube was able to show by 

 demonstrating that the inflammation could be prevented by permitting the ani- 

 mals to breathe through a tracheal cannula introduced through an external wound 

 in the neck. If, however, only the motor filaments of the recurrent nerves were 

 divided, and the esophagus was ligated, so that foreign bodies necessarily entered the 

 air-passages, so-called foreign-body pneumonia resulted in an analogous manner, 

 with a fatal termination. (6) A second factor resides in the fact that in conse- 

 quence of the extensive and labored snoring and noisy breathing, the lungs must 

 become hyperemic, as during the protracted and marked dilatation of the chest 

 the pressure of the air in the lungs must be abnormally low. As a result, serous 

 transudates (pulmonary edema) result, or even extravasation of blood and dilata- 

 tion of the pulmonary vesicles at the margins of the lungs. Through this influence 

 the entrance of foreign bodies, particularly of fluid, into the glottis is facilitated. 

 A tracheal cannula introduced from without will likewise prevent the inflammation 

 under these circumstances, (c) Perhaps partial paralysis of the pulmonary 



