318 RESPIRATION. 



mucous lining of the air-passages is reddened (especially in 

 dogs), the color being due to the injection of the capillaries of 

 the raucosa with blood. The lungs collapse much less than 

 naturally when the chest is opened. The pulmonary paren- 

 chyma is, to a greater or less extent, devoid of air. The air- 

 less parts are soaked with a brownish-red serous liquid, and 

 here and there choked with a grayish- white material, which, on 

 microscopical examination, is found to consist of young cells 

 (pus corpuscles). Similar cells are seen in the serous liquid 

 along with numerous blood corpuscles. These changes may 

 be accounted for as follows : When the vagi are divided, all 

 the parts to which the branches below the point of section are 

 distributed are affected, e. (/., the larynx, air-passages, lungs, 

 oesophagus, etc. 1. The glottis is partially closed, just as it is 

 after death. 2. The mucous lining of the air-passages is de- 

 prived of sensibility, so that, when it is irritated, no cough is 

 produced. 3. The muscular fibres of the oesophagus are para- 

 lyzed, so that regurgitation of food from the stomach is apt 

 to take place ; the muscular fibres of the bronchial tubes are 

 in a similar condition. With reference to these co-efficients in 

 the production of the lung affection we have the following 

 facts, showing that the first two are at all events the only ones 

 which are of importance: (a) A lung affection of the same 

 nature as that induced by section of both vagi, though of in- 

 ferior intensity, follows section of the inferior laryngeal 

 nerves. (6) In animals with divided vagi, life is prolonged 

 by tracheotomy, the degree of prolongation depending on the 

 efficiency of means used to prevent the entrance of foreign 

 bodies into the air-passages, (c) In animals of which the vagi 

 are intact, a lung affection is produced by injecting mucus 

 from the pharynx into the air-passages which is of the same 

 nature with that now under consideration. The combination 

 of these facts leads to the inference that the inflammation of 

 the lungs of which animals with divided vagi die, is dependent 

 on the intrusion of foreign bodies from the pharynx into the 

 air passages and lungs, rather than to anj T direct effect of the 

 section on the lung tissue. 



102. Demonstration of the Respiratory Functions 

 of Afferent Fibres of the Vagus, by Excitation of the 

 Central End of the Divided Nerve. -The method of 

 preparing the nerve has been already described. The excitor, 

 shown in fig. 225, is used. It is better to employ Helmholtz's 

 side wire (see next paragraph), but not necessary ; for even, 

 when strong unmodified induced currents are used, there is 

 little danger of unipolar effects, the extent to which the nerve 

 can be separated being such, that there is no difficulty in inter- 

 posing a considerable air space between it and the surrounding 

 parts. 



