168 MANUAL OF EQUINE MEDICINE. 



the chest is round the thoracic movements are more limited, 

 and the horse will in consequence not be able to take deep 

 inspirations or make strong expiratory efforts. 



The nervous or functional derangement of the bronchial 

 tubes and air-vesicles is soon succeeded by structural 

 changes. The latter become inflated, and thus the circula- 

 tion in the capillary blood-vessels is impeded, and the 

 nutrition of the bronchial mucous membrane and muscles, 

 and the walls of the vesicles themselves, becomes impaired 

 (AYilliams). 



Degeneration of these structures now follows, and the 

 lungs become more and more emphysematous, the air- 

 cells are dilated, their walls are stretched, and air now 

 becomes intercalated among the connective-tissue of the 

 lung. 



In this manner vesicular and interlobular emphysema ma}^ 

 frequently be produced. The right side of the heart may 

 become hypertrophied and dilated in consequence of these 

 changes in the lung structure. 



The dyspnoea of broken wind seems to result from the 

 emphysematous condition of the lung, as well as from general 

 impairment of the contractile power of the pulmonary 

 organs. 



Having now reviewed the proximate causes of broken 

 wind, we may now consider the more remote causes. 



They are : 



(1.) Heredity. — The offspring may inherit the same 

 bodily conformation and temperament as their parents, and 

 thus be more liable to become similarly affected. 



(2.) Dietetic. — Defective dietetic conditions are largely 

 responsible for the production of broken wind. As the 

 diet of the coarser breed is frequently innutritious and 

 bulky, and the animals often worked after a heavy meal 

 with full allowance of water, they are more frequently 



