472 DISEASES OF THE LUNGS. 



action, we speak of the process as Bronchitis ; when the paren- 

 chyma, or true vesicular substance of the lungs, is the seat of 

 the disturbance, the disease is called Pneumonia ; while when 

 the action is chiefly located in the serous membrane covering 

 the lungs, or the thoracic Avails, the condition is known as 

 Pleuritis. 



Very rarely, however, in practice do we find that these 

 several diseased conditions are distinctly and sharply marked 

 out from each other ; it is more frequently, if not invariably, 

 the case that they are variously combined and shaded into 

 each other, the morbid condition of one particular structure 

 most probably holding a suflicient prominence and distinctive- 

 ness to give to the entire state its leading and characteristic 

 features. 



It is seldom that in veterinary practice we encounter in any 

 of our patients inflammation of the lung-tissue proper — pneu- 

 monia — without at the same time finding the air-tube, large or 

 small, more or less implicated — bronchitis — constituting the 

 condition we recognise by the term pneumonia-bronchitis, or 

 broncho-pneumonia ; or when the air-tubes have in a great 

 measure escaped the inflammatory action we find, along with 

 the pneumonia, an inflamed condition of the investing 

 membrane, the pleura, the condition known as pleuro-pneu- 

 monia. 



It is not, therefore, to be expected in the study of pneu- 

 monic diseases, as they are presented to us in the living 

 animal, that we will usually observe any one of these separate 

 and distinct structures alone and of itself invaded by the 

 diseased action ; we may, however, by attention to the symp- 

 toms and phenomena specially distinctive of diseased action in 

 these individually, become the better able to determine how 

 far each is involved in any morbid condition in which they 

 severally participate. , 



