DISEASES OF THE RESPIRATORY ORGANS. 223 



eive inflammation is not common, and is almost of neces- 

 sity fatal. Pneumonia is divided into lobar {croupous, 

 diffuse) and lobular {patchy, catarrhal). In the latter, 

 only limited and usually scattered portions of the lung 

 tissue are involved. This form is most common as a com- 

 plication of bronchitis, and especially when it arises in 

 the course of other diseases. 



Causation. — The onset is favored by wet, cold, any- 

 thing inducing a chill, etc. Some cases are almost cer- 

 tainly due to a microbe, and the disease then seems to be 

 infectious. It will be safe in treatment to regard all cases 

 as infective. 



Pathology. — In lobar pneumonia we have a typical 

 inflammation with hypergemia, soon followed by escape of 

 red and white corpuscles from the blood-vessels, and effu- 

 sion of a coagulable fluid with increase {proliferation) of 

 the lining and other cells of the tissue of the lung. The 

 portion of lung involved gets red and solid, when removed 

 after death, sinks in water, cuts firm, and looks not unlike 

 liver. This is the stage of red hepatization, and is suc- 

 ceeded, when the course of events is typical, by a fatty 

 degeneration of the morbid products, a stage known as 

 gray hepatization. Resolution is the return to the nor- 

 mal by the absorption or removal of this foreign material, 

 a natural state of the blood-vessels, etc. Untoward results 

 may occur, abscess or purulent infiltration — i. e., breaking 

 down of the lung tissue — and gangrene or local death, 

 usually followed by breaking down of a portion of the 

 lung. Both the latter conditions frequently prove fatal. 

 With pneumonia there is usually more or less bronchitis, 

 and often pleurisy. 



