312 PULMONARY MUCOUS TISSUE. 



undergoes in pathological cases. The respiratory murmur 

 is evidently caused^ by friction against the sides of the air- 

 vessels, but it is not easy to decide exactly where this mur- 

 mur is localized. It was formerly attributed to the unfolding 

 of the pulmonary vesicles, whence the name of vesicular 

 murmur. Beau, however, maintains that its seat is at the 

 opening of the glottis; many physiologists have adopted this 

 opinion, while Bergeon has recently (1869) combined the 

 two theories, slightly modifying both, lie holds that the 

 inspiratory sound is produced in two places, the glottis and 

 the lung, while the expiratory sound is produced in the 

 glottis only ; the former being caused by the passage of the 

 air through the constricted orifices, this passage being accom- 

 panied by the formation of fluid, vibrating veins (see Circu- 

 lation, p. 164) ; these veins are formed both at the glottis and 

 at that of the opening of the small bronchi into the pul- 

 monary alveoli. The cause producing the respiratory sounds 

 cannot be supposed to exist only at the level of the glottis, 

 for the sound continues the same in cases in which the air no 

 longer passes through the larynx, as after operations in 

 tracheotomy. We may, therefore, conclude that the causes 

 of the respiratory murmur are manifold, and the principal 

 one may be said to be (Sabati.er) the dull crepitation pro- 

 duced by the detachment of the trabeculae, or slightly 

 moistened partitions of the pulmonary alveoli ; the vibra- 

 tions made in the air at the sharp edges formed by the bron- 

 chial bifurcations ; the friction of the air against the bronchial 

 coats ; and, finally, the more or less decided resonance of the 

 superior or glottic sounds. 1 



B. Mechanical effects produced by respiration in the organs 

 adjacent to the lungs. 



The mechanical consequences of the inspiratory and cx- 



5 iratory movements are not confined to the air-vessels ; the 

 lood vessels and the circulation of the blood are also affected 

 by these movements, the greater part of the circulating 

 system being contained in the cavity of the thorax. 



We have represented the circulation in a diagram, by the 

 figure of 8, the upper half representing the pulmonary circu- 

 lation, and the lower, the general circulation, the point of 



1 See " Les Nouvelles Recherches," de V. Cornil; " Anatoraie 

 Pathologique et Auscultation du Poumon." Mouveinent medical, 

 Avril et mai, 1873. 



