492 PNEUMONIA. 



non-existencG, comparatively speaking-, of organizablo exudate, 

 and the extent of alveolar and endothelial proliferation so 

 characteristic of catarrhal inflammation of mucous membranes, 

 and because of its limited diffusion as compared with the 

 lobar, being confined to lobules or collections of lobules. 

 3. Interstitial j^^'^eiimonia, when the action is believed to be 

 confined to the interlobular connective- tissue of the alveoli of 

 the lungs, and to result in thickening of the walls of the 

 alveoli and of the interconnective-tissue. 



li is also spoken of as primiary imeumonia when the 

 diseased process appears to originate in or from the lung- 

 tissue, independently of association directly as an inducing 

 cause with any other diseased condition ; as secondary i^neuino- 

 nia when the inflammatory state of the pulmonary structures 

 succeeds to, or is believed to proceed from, some antecedent 

 unhealthy condition. It is also styled specific pneumonia 

 when accompanying such specific diseases as glanders-farcy. 



Of these different forms of inflammation of lung-tissue, it is 

 of the commonly occurring, independent inflammation in- 

 vading the entire pneumonic structures, ordinary exudative or 

 lobar pneumonia, that we would chiefly now speak ; of that 

 which is par excellence pneumonia. 



It is, however, deserving of notice that the form and cha- 

 racter of the diseased action is much modified in those crea- 

 tures which severally come under our notice, by the variations 

 which we observe in the anatomical structure of the lungs of 

 these individually. In the horse, where the interlobular tissue 

 is comj)aratively small in amount, the inflammatory action is 

 more truly catarrhal than croupous ; in the greater number of 

 instances the inflammatory products accumulate largely in the 

 interior of the air-vesicles. In the ox the conditions are 

 reversed, the exudative character of the action being a pro- 

 minent feature. 



h. Nature and Causation. — Ordinarily, and by the majority 

 of observers, pneumonia has been regarded as merely a local 

 diseased condition — inflammatory action — with which the 

 more or less highly developed pyrexial state was to be regarded 

 simply in the relation of cftect to cause, as truly an expected 

 symptom of the local tissue-change. There are, however, others 

 who regard the entire morbid conditions and changes in a very 



