388 Veterinary Medicine. 



INFLAMMATION OF THE MEDIASTINUM : MEDIASTINITIS. 



This may be acute or chronic, simple or infectious, primary or 

 secondary. It is usually concentrated in the lymph glands, yet 

 it may extend around these, or, starting independently in the 

 lymph plexuses, it may lead to extensive exudation and infiltra- 

 tion of the connective tissue, with subsequent organization and 

 contraction which compresses important organs and impairs vital 

 functions. This may compress the heart, interfering with its 

 normal functions, but much more frequently it acts through ob- 

 struction of the vena cava, with consequent tardy movement 

 through the jugulars and capillary congestion of the neck and 

 head or of the fore limb : or it lessens the calibre of the pulmo- 

 nary veins, threatening congestion of the lungs and causing dys- 

 pnoea ; or again it obstructs the aorta or pulmonary artery, causing 

 irritability and irregularity of the action of the heart, with 

 hypertrophy or dilatation ; or again it compresses the vagus or 

 sympathetic nerve, producing hepatic, gastric or intestinal dis- 

 order ; or compressing the left recurrent laryngeal nerve it leads 

 to paralysis and wasting of the arytenoid muscles of the larynx 

 with stridor (roaring) in forcible inspiration ; or it presses on 

 the gullet, interfering with deglutition and eructation, and pro- 

 ducing indigestion and tympanies. 



In the more acute cases in which the phlegmonous inflammation 

 eventuates in abscess, this may become enclosed in thick fibrous 

 walls as a permanent source of dyspnoea, or more commonly it 

 breaks into the pleural cavity, producing empyema ; or it may 

 break through the foramen dextrum or synistrum into the abdomi- 

 nal cavity with fatal results ; or, more happily, it may burrow 

 toward a bronchial tube and discharge through that, or between 

 the two first ribs so as to escape at the lower part of the neck. 



In horses such acute cases are usually manifestations of 

 irregular strangles, but they may also supervene on pneumonia, 

 croupous or contagious, on infectious bronchitis, on pleurisy, on 

 pericarditis, on influenza, or even on other pyogenic infec- 

 tion. The chronic cases are more likely to coincide with 

 glanders, tubercle, actinomycosis, hydatids, linguatula, or neo- 

 plasms — simple or malignant. 



In cattle. Acute cases may result from perforation of the 



