THE RESPIRATORY SYSTEM. 489 



The formation of exudates is favored by the extensive capillary network which is 

 almost directly exposed to such deleterious agents as may gain access to the air spaces ; 

 while a great accumulation of exudates is possible owing, to the spongy structure of 

 the organs. 



The transitional character of the epithelium lining the air vesicles predisposes to 

 cell proliferation and exfoliation, and thus to the formation of exudate. 



On the other hand, the abundant blood and lymph channels 1 favor the ppeedy re- 

 moval from the air spaces in the lungs of large quantities of exudate. 



While the abundant lymphatics of the lungs aid in the rapid disposal of exudates, 

 they, on the other hand, favor the absorption of toxic substances into the body at large 

 when bacteria, for example, are the excitants of the local inflammation. 2 So that al- 

 though exudative pneumonia is commonly considered a local disease, it is often rather a 

 local expression of a general infection or is doubly significant on account of the asso 

 ciated toxaemia. 



In addition to the development and accumulation of exudates, necroses and the 

 formation of fibrous tissue are the most noteworthy general pathological processes it 

 the lungs. 



While the conspicuous differences in the various forms of pneumonia are largely 

 due to differences in the nature, virulence, and distribution of their excitants, predis- 

 posing factors dependent upon age, constitutional condition, and the protective mechan- 

 ism of the lungs are of great significance. 



The common classifications are based partly upon etiology, partly upon morphol- 

 ogy, and the names used suggest now the topography of the lesions or the character ox 

 the tissue which is especially affected, and again the species of the bacterial excitant. 

 Thus the term lobar pneumonia is topographical ; tuberculous pneumonia emphasizes 

 the excitant ; while interstitial pneumonia suggests the form of tissue involved. 



ACUTE LOBAR PNEUMONIA. (Fibrinous Pneumonia Croupous 

 Pneumonia. ) 



This is an infectious disease incited by the Micrococcus lanceolatus 

 (pueumococcus of Fraenkel). 8 It is especially characterized by an exu- 

 dative inflammation in which red and white blood cells, serum, and fibrin 

 accumulate in the air spaces of the lungs, usually involving, especially in 

 adults, the whole of one lobe or lung or portions of both lungs.* Toxae- 

 mia from the absorption of poisons formed locally in the lungs is an 

 important and often most significant factor in the disease. The pnemno- 

 coccus is occasionally widely disseminated in the blood. 



During the first hours of the inflammation the capillaries of the air 

 spaces are congested, the lung is oedematous, firmer than normal, but not 

 markedly consolidated. The air spaces contain varying numbers of leu- 

 cocytes, red blood cells, serum, and fibrin (Fig. 270). The epithelial 



1 See Miller, Arch. f. Aaat. und Physiologic, Anat. Abth., 1900, p. 197, bibli- 

 ography. 



2 Note by Councilman, "The Lobule of the Lung and its Relation to the Lym- 

 phatics," Boston Jour. Med. Sciences, vol. iv., p. 165, 1900. 



3 We shall use here as synonymous the names Micrococcus lanceolatus and pneumo- 

 coccus; when pneumococciis is used the pneumococcus of Fraenkel is referred to. For 

 a description of this organism see p. 191. 



4 The clinical course and the morphological characters of the inflammation of the 

 lungs associated with the Micrococcus lanceolatus are so typical that we seem justified 

 in limiting the term lobar or fibrinous pneumonia to this condition, even though inflam- 

 mations of the lungs due to other excitants are occasionally lobar in extent and may 

 have a fibriuous exudate, and though exceptionally the pueumococcus inflammation 

 itself fails to reach lobar proportions. 



