DISEASES OF THE BRONCHI. 145 



gradually becomes less severe as the secreted mucus becomes 

 thinner and clearer, and finally disappears. 



Bronchitis of the larger tubes is not generally a fatal 

 disease ; but when affecting the smaller bronchial ramifica- 

 tions and pulmonary vesicles, especially if there be pro- 

 fuse discharge of yellowish matter, which blocks up and 

 occludes the small tubes and air-cells, the prognosis is very 

 serious. 



Secondary Bronchitis. — Is sometimes met with in rheuma- 

 tism, glanders, 'and in young horses suffering from scrofulous 

 arthritis it is a common complication, and is here found in 

 conjunction with pulmonary embolism ' (Robertson). 



In these cases the bronchial symptoms are usually mani- 

 fested during the progress of the primary disease. 



Mechanical Bronchitis. — The symptoms of this form of 

 bronchitis vary much with the nature of the cause, and are 

 similar to those of acute catarrhal bronchitis. Mechanical 

 bronchitis is induced by some irritant in contact with the 

 lining membrane of the tubes. The irritating agent may be 

 gaseous, as, for instance, smoke from burning buildings or 

 acrid fumes ; or it may be fluid or solid, as, for instance, 

 food or other matters finding their way into the air-tubes. 

 Mechanical irritation in some instances causes the condition 

 known as plastic bronchitis, in which laminated fibrinous 

 casts are formed in the air-tubes, and block up the lumina, 

 thus inducing serious pulmonary mischief. 



Morbid Anatomy of Bronchitis. — Inflammation of the 

 bronchial tubes is attended with changes in the epithelial 

 covering, glandular secretions, and in the subjacent tissues. 



The mucous membrane is congested, sometimes intensely 

 so, and undergoes more or less infiltration and thickening. 

 It may acquire a granular aspect and soft pulpy consistence. 

 The inflammation may be limited to the surface of the mucous 

 membrane, but often pervades the sub-mucous tissues, in. 



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