CHAPTER IV. 

 DISEASES OF THE LUNGS. 



CIRCULATORY DISTURBANCES IN THE LUNGS. 



Congestion of the Lungs. — Definition. — An engorgement of 

 the pulmonary capillaries with blood. It may be active or 

 passive. 



Etiology. — Active congestion is due to increased heart 

 action which may be brought about' by overexertion in 

 unconditioned horses (racing, hard pulling) especially during 

 hot weather. Heat stroke may induce it. The inhalation 

 of irritant gases (stable fires) is a cause. The first stage of 

 pneumonia is congestion of the lungs. 



Passive congestion: Two forms may be recognized, 

 mechanical and hypostatic. 



Mechanical congestion occurs whenever there is some 

 condition of the heart present which prevents the free return 

 of blood to it (left valvular stenosis; mitral insufficiency). 

 It may arise from any heart's weakness (cloudy swelling, 

 dilatation), and occur during the course of an acute infectious 

 disease which affects the heart. Passive congestion may 

 follow filling of the' pericardium (pericarditis) and be second- 

 ary to gastric or intestinal bloat. 



Hypostatic congestion occurs in large animals when the 

 patient lies in one posture for a long time, the blood gravitat- 

 ing to the lower lung. Probably the attending heart's 

 weakness assists. 



PULMONARY EDEMA. 



Definition. — A transuding of serum into the alveoli and " 

 bronchioli. It is the next step in congestion, which it 

 accompanies; it also occurs in pneumonia. 



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