Asthma. Broken Wind. Heaves. Dyspnoea. 279 



This retention of air in the hings during violent compression of 

 the chest walls is precisely the condition met with during an 

 access of coughing, and in both cases alike there is the tendency 

 to overdistension of the minute tubes and air cells until they have 

 lost their power of contraction, or they may even give way and 

 allow the air to pass out and lodge in the lung tissue. 



Another mode in which violent effort injures the lungs is by 

 the rapid and continued inhalation of great quantities of air dur- 

 ing rapid breathing, so as to dilate the lungs suddenly to their 

 fullest extent. Sometimes from irregular distribution of the 

 serial current or from the want of tone in a particular part of the 

 lung that gives way under the pressure and the air cells become 

 overdistended or ruptured. This condition is especially met in 

 the more rapid paces. It is well exemplified in the results of the 

 deep breathing after cutting the vagi nerves. 



In either case the result will be more certain if the effort is 

 made upon a full stomach or with the functions of the vagus 

 nerve impaired by a previous faulty diet. 



That broken wind is a frequent concomitant or sequel of 

 ehronic bronchitis is undeniable, and theoretically nothing is more 

 likely to cause dilatation and rupture of the air cells and conse- 

 quent impairment of the innervation and contractility of the lung 

 than violent fits of coughing, while the bronchial tubes have 

 thickened and friable walls, or are partially plugged by tenacious 

 mucus. 



Broken wind is mainly a disease of old horses, though I have 

 seen several cases in five-j^ear-old animals, and Bouley records a 

 case in a two-year-old colt out of a badly broken-winded mare. 

 This would seem to indicate an hereditary proclivity, and there 

 is no doubt that the shallow, narrow, weak che.st predisposing to 

 this as to many other pulmonary complaints is transmitted from 

 parent to offspring. 



Nature of the Disease. Emphysema of the lungs is the most 

 constant structural change met with in the bodies of animals 

 which have suffered from broken wind. This condition of the 

 horse's lung appears to have been noticed by the early Greek, 

 writers. It was advanced as the cause of broken wind by Riding 

 in 1704 (Pathologic Veterinaire), by Floyer in England in 1761 

 (Treatise on Asthma in Man), by Vitet in France in 1783 (Medi- 



