144 PRACTICE OF EQUINE MEDICINE. 



Give the forms. 



There are two principal forms — the vesicular and the interlob- 

 ular. 



What is the difference ? 



The vesicular form is a simple dilatation of the alveoli and 

 lobules, with atrophy of the interalveolar walls, while the intervesic- 

 ular or iriterstitial form is a rupture of the walls of the air-cells, 

 and the air escapes into the connective tissue wliich binds the air- 

 cells together. There is an increased intralobular pressure, causing 

 air to gain entrance into the interlobular connective tissue and into 

 the lymphatic spaces. 



What is the aetiology ? 



In the human subject, violent efforts at coughing, where the 

 bronchial tubes are filled with mucus. 



Men who play wind instruments or do heavy lifting suffer with 

 emphysema. 



In the horse, rapid work, heavy draft work, may be a cause. 



There is also a hereditary predisposition, there being a weak- 

 ness in the walls of the air-cells. 



An animal driven for some distance at the top of his speed 

 (he being a willing horse) will overdo himself, and the residual air 

 has a tendency to dilate the air-cells. 



If drawing a heavy load, more muscular work must be per- 

 formed; this causes a deep inspiration and a closure of the glottis, 

 and the air becomes heated and dilates and stretches the waDs of 

 the air-cells. 



Coughing may cause it also, but it takes some time to produce 

 it in this way. 



The feeding of dusty or dirty hay or bulky food is also said 

 to produce it; in the country they often feed dry hay, straw, corn- 

 stalks during the winter, and in the spring the horse may be heavy. 



It may follow pneumonia, pleurisy, etc. 



What are the post-mortem appearances ? 



On opening the thorax, a striking difference in the appearance 

 of the lungs is seen; instead of collapsing, as they do normally, the 

 lungs remain full, and even, in severe cases, may bulge up, as if they 

 were being inflated; tliey are soft and downy to the feel, of a rosy 

 tint, but lighter than normal; they do not contain so much blood. 



