208 CHAPTER 22. 



pharynx and larynx will continue to be for some time very susceptible of 

 irritation and inflammation. Great attention must also be given to the 

 ventilation of the stable. 



When the discharge from the nostrils continues for a length of time, 

 even after the horse has in other respects recovered, the case must be 

 treated as one of Nasal Gleet. See Chapter 25. 



BRONCHITIS, PNEUMONIA, PLEURITIS, AND PLEURO- 

 PNEUMONIA. 



423. Structure of the organs affected. 



Before treating of Bronchitis, Pneumonia, Pleuritis, and Pleuro-pneu- 

 monia, it will be necessary to glance briefly at the structure of the organs 

 affected in these diseases. 



424. Structure of the Lungs and Broncliide. 



The lungs are contained in the chest or large cavity in the anterior 

 portion of the body. The sides of the cavity are formed by the ribs, its 

 top by the spine or back bone, its front by the sternum or breast bone, 

 whilst posteriorly it is separated from the stomach and intestines by a 

 flexible curtain called the diaphragm. Further protection is afforded to 

 the cavity by the shoulder-blade bones. 



The lungs consist of two soft elastic masses, which fill the cavity of 

 the thorax. The right mass of the lungs has four lobules, whilst the left 

 has only three. The interior walls of the cavity and the lungs themselves 

 are covered with a fine serous membrane called the pleura. The lungs 

 are in constant motion during life, enlarging and diminishing during the 

 acts of inspiration and expiration. The mass of the lungs is made of 

 innumerable minute cells, connected together by cellular tissue. 



The lungs are connected with the external air by means of the nostrils, 

 larynx, and trachea or windpipe. This latter organ runs at first as a 

 single tube, but after entering the chest it divides into two branches 

 called the Bronchial tubes. They are similar in structure to the wind- 

 pipe. They divide again and again, and subdivide and ramify through 

 the lungs, gradually becoming more and more minute. They terminate 

 all through the lungs in the minute air cells. Over the surface of these 

 cells the capillary ramifications of the pulmonary arteries are spread in 

 exquisite minuteness, and here the blood imbibes from the air its oxygen. 

 The pulmonary veins receive from the surface of the cells the blood which 

 has been thus oxydised, and return it to the heart. 



If the air supplied to the lungs is impure, the oxydising process cannot 

 be efficiently performed. Again, if from disease or other cause the 

 passage of the air through the lungs is impeded, and the supply is thereby 

 lessened, the purification of the blood will be imperfect. 



It is chiefly on this latter account that we have so often impressed on 

 the reader the necessity of an ample supply of the best and purest air to 



