ACUTE DISEASES OP THE OEGANS OF EESPIEATION. 209 



all horses suffering from diseases of the respiratory organs. A supply 

 which may be quite sufficient in health, when the air has free course 

 through every part of the lungs, may be very insufficient when portions 

 of the respiratory system are impeded. 



Each lung, as stated above, is divided into two great divisions or lobes. 

 Disease may exist in one lung or in one lobe without materially affecting 

 the other ; but this is very seldom the case in horses, because all inflam- 

 matory diseases run their course very rapidly, and therefore in a very 

 short time the whole substance of the lungs is generally involved. Hence 

 it is quite common for horses to die after suffering for only two or three 

 days from diseases of the pleurae or lungs. 



425. Structure of the pleurse. 



Every part of the entire substance of the lungs as well as of the cavity 

 of the chest is lined with a fine serous shining lubricating membrane 

 called the Pleura. This membrane prevents the different portions of the 

 lungs from adhering to each other, and also prevents the lungs themselves 

 from adhering to the sides of the cavity of the chest. Thus by means of 

 the Pleurse their free and easy motion without friction is ensured at each 

 respiration. The portion of the pleura which lines the ribs is termed the 

 pleura costalis, whilst that which invests the lungs is called the pleura 

 pulmonalis. 



426. Different seats of disease. 



Inflammation may attack one or all of these structures, namely the 

 bronchi, the lungs, or the pleurae. The disease takes its name from the 

 part affected. Thus if the bronchi only are attacked, the disease is 

 called Bronchitis ; if the pleurae only, Pleuritis ; if the lungs only, Pneu- 

 monia ; whilst if both lungs and pleurae are simultaneously attacked, the 

 disease bears the compound name of Pleuro-pneumonia. 



Bronchitis is often found as a separate disease, but in bad cases it may 

 become complicated with pneumonia. Pleuritis and pneumonia, though 

 occasionally found as separate diseases, more often occur in conjunction, 

 constituting Pleuro-pneumonia. 



427. Certain formations of Chest predisposed to disease. 



Though we believe, as stated above, that diseases of the respiratory 

 organs generally have their origin in preventible causes, yet we must at 

 the outset admit that certain formations of chest entail a greater liability 

 than others to disease. Even here, however, the owner is mainly 

 responsible. It is his own fault, if he subjects an animal to work and 

 wear for which his physical formation renders him unfit. 



A shallow and flat-sided chest, for instance, does not afford sufficient 

 capacity for the lungs to enable the animal to perform fast work. If such 

 work is required of an animal so formed, there will be great liability to 

 disease of the Respiratory organs. 



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