530 PLEURISY. 



well aware that morbific influences, whether operating intrin- 

 sically or extrinsically on animals, are frequently accompanied 

 with specific inflammations of serous membranes generally. 

 Still we cannot ignore the fact, that in many instances pleurisy, 

 in the animals which more properly come under our considera- 

 tion, shows itself in situations and under conditions where its 

 existence is most satisfactorily explained by referring it to the 

 direct and immediate action of cold and exposure. 



It is a tolerably safe assertion to make, that pleurisy is chiefly 

 owing to the presence in the animal system of some specific 

 morbific agent, seeing such is often difficult to disprove. At the 

 same time we are Avell aware that it not unfrequently appears 

 as an accompaniment of such constitutional disturbances and 

 states of ill-health as pyemia, suppurative arthritis, or sup- 

 purative phlebitis ; that it is well known under certain not 

 understood and ill-defined conditions of both enzootic and 

 epizootic influences. 



Still, notwithstanding the evidences and the probabilities, 

 which together are strong, that in many cases of pleurisy suc- 

 ceeding exposure to cold, there exists in the animal affected 

 some specific diseased condition tending to particular localiza- 

 tion of diseased action in special serous structiu'es, it is difficult 

 to persuade those who have often witnessed its succession in 

 the horse to severe exertion, attended with subsequent ex- 

 posure, that this same latter influence was not the chief and 

 direct agent in the production of this inflammatory state, apart 

 altogether from indwelling morbid conditions. 



4. Blood-contaminations as appearing in certain Specijic 

 and Gonstitiitional Diseases. — The influences and agencies 

 represented by this last group of causes are, without doubt, 

 extensive and ever existing, although often inappreciable save 

 by their results. They include all which are spoken of as 

 diathetic, dietetic, infective, enzootic, and epizootic ; and have 

 their representative results in association with such diseases as 

 rheumatism, pyiemia, and some specific fevers. 



h. Anatomical Characters. — Ordinarily, and in health, the 

 pleura is an all 'but colourless membrane in itself, the colour 

 which we may imagine it to possess when viewing it in situ 

 being conferred upon it from subjacent textures and vessels. 

 When involved in inflammation the })leural vessels show them- 



