488 THE RESPIRATORY SYSTEM. 



the gangrenous portion of lung assumes a dirty green color and a putrid 

 odor. It becomes soft, disintegrated, and separated from the surround- 

 ing lung. The blood-vessels may be obliterated by thrombi, or eroded, 

 so that there are profuse haemorrhages. 



Such a gangrenous process may extend to the adjacent lung tissue, or 

 a zone of gray or red hepatizatiou or of connective tissue may be formed. 

 The fluid from the gangrenous lung may pass into the bronchi and be 

 expectorated ; or it may run from one bronchus into another and incite 

 new gangrenous foci or diffuse gangrene. The pulmonary pleura may be 

 perforated and a gangrenous pleurisy produced. Gangrene may follow 

 lobar or broncho-pneumonia, especially such phases of the latter as result 

 from the inspiration of foreign material containing micro-organisms from 

 the mouth ; it may arise from infectious emboli in the lungs, or by an 

 extension of a gangrenous process from an adjacent part. It may be as- 

 sociated with oesophageal diverticula. * 



Diffuse gangrene may follow the circumscribed form ; it may compli- 

 cate lobar pneumonia or occur as an independent condition. A large 

 part of a lobe or of an entire lung becomes greenish, putrid, and soft, 

 and the pulmonary pleura is inflamed. There may be haemorrhages from 

 eroded vessels. There may be general septicaemia. 



Various forms of bacteria may be present in gangrenous areas of the 

 lungs. Among the more common are Streptococcus pyogenes, Staphy- 

 lococcus pyogeues, pneumococcus, and various saprophytic micro-organ- 

 isms. 11 



INFLAMMATION. (Pneumonia, Pneumonitis.) 

 General Considerations. 



Before commencing the study of inflammation of the lungs it is well to recall some 

 of those features of structure and function which influence the local manifestations of 

 disease in these organs and largely determine the special character of its lesions. In 

 the first place, the lungs, like the gastro-intestinal canal, while in a topographic sense 

 within the body, are still in open communication with the exterior, and are thus m^ rn 

 directly exposed to various deleterious agencies than are those structures and organs 

 wholly enclosed by living tissues. Notwithstanding this vulnerability of location, the 

 recesses of the lungs are guarded by protective mechanisms of great efficiency. Thus 

 in normal respiration the air, which often bears as dust many organic and inorganic 

 substances as well as minute living organisms; is largely cleansed by its repeated im- 

 pingement upon the moist mucous surfaces of the nose, pharynx, larynx, and bronchi. 

 The ciliated cells of these membranes are constantly sweeping upward such of these 

 particles as have lodged upon them, while by the lymph channels and the lymph nodes 

 foreign substances which have escaped the barriers are either removed or stored in the 

 least harmful situations. Damage to the integrity or efficiency of these protective 

 agencies is a factor in the origin of pulmonary diseases too often ignored. 



The responses of the lung tissues to the excitants of inflammation are not funda- 

 mentally as distinct nor as variable as the common classifications of pneumonia would 

 seem to indicate. Exudation from the smaller blood-vessels is one of the most common 

 features of the acute phases of pulmonary inflammation. 



1 See reference to Stnrck, p. 531. 



2 See for "acid-proof " bacilli in srangrene, Ophuls, Jour. Mecl. Res., vol. viii., p. 

 242. 



