344 DISEASES OF THE RESPIRATORY ORGANS. 



Bacteria play an important part in the production of 

 catarrhal pneumonia, though no one organism is recognized 

 as the specific cause. In a large percentage of cases FriinkePs 

 pneumococcus is found. 



Lesions: The inflammatory process seems always to begin 

 in the terminal bronchioles, and to extend by contiguity and 

 continuity to surrounding lung-tissue. 



Scattered through both lungs there is a variable number 

 of solid patches, some of which are due to collapse of the air- 

 vesicles, while some are the result of inflammatory exudation. 

 The collapsed areas vary from one -tenth to one-fifth of an 

 inch in diameter, and are depressed below the surface of the 

 lung-tissue. The pneumonic patches vary from the size of a 

 pea to that of a hazelnut or walnut, and are raised above the 

 surface ; the overlying pleura may be somewhat opaque from 

 inflammatory exudation ; the surrounding pulmonary tissue 

 is often more or less emphysematous. 



As a whole the lungs are congested but crepitant ; the solid 

 patches, however, are airless and sink in water. On section 

 the areas of collapse are found to be more or less conical in 

 outline, with the apex directed toward the bronchi with which 

 they are connected. The pneumonic patches are soft and 

 friable, at first dark red, and later grayish-yellow in color ; 

 they are not separated by a sharp line of demarcation from 

 the surrounding tissue. By the coalesence of such patches 

 nearly a whole lobe may be involved, in which case it is often 

 difficult to distinguish from the consolidation of a lobar 

 pneumonia. The cut surface of such an area is smooth, how- 

 ever, not granular ; irregular in outline ; and there are 

 neighboring smaller areas which have not as yet become fused 

 to the larger one. 



The inflammatory process is sometimes divided into two 

 stages, red and gray splenization. corresponding to red and 

 gray hepatization of the lobar variety. 



Microscopically , in the early stage of red splenization, if a 

 single lobule is examined, we note in the centre a small 

 bronchus with infiltrated, thick walls ; its lumen may be 

 filled with leukocytes and desquamated epithelial cells. The 

 interlobular connective tissue and alveolar walls are also 

 infiltrated and thickened by proliferating connective-tissue 



