DISEASES OP THE LUNGS. 137 



HEAVES, BROKEN WIND, OK ASTHMA. 



Much confusion exists in the popular mind in regard to the nature 

 of heaves. Many horsemen loosely apply the term to all ailments 

 where the breathing is difficult or noisy. Scientific veterinarians are 

 well acquainted with the phenomena and locality of the affection, but 

 there is a great diversity of opinion as regards the exact cause. 

 Asthma is generally thought to be due to spasm of the small circular 

 muscles that surround the bronchial tubes. The continued existence 

 of this affection of the muscles leads to a paralysis of them, and the 

 forced breathing to emphysema, which always accompanies heaves. 



Heaves is usually associated with disorder of the function of diges- 

 tion or to an error in the choice of food. Feeding on clover hay or 

 damaged hay or straw, too bullcy and innutritious food, and keeping 

 the horse in a dusty atmosphere or a badly ventilated stable produce 

 or predispose to heaves. Horses brought from a high to a low level 

 are predisposed. 



In itself broken wind is not a fatal disease, but death is generally 

 caused by an affection closely connected with it. After death, if the 

 organs are examined, the lesions found depend much upon the length 

 of time broken wind has affected the animal. In recent cases very 

 few changes are noticeable, but in animals that have been broken- 

 winded for a long time the changes are well marked. The lungs are 

 paler than natural, and of much less weight in proportion to the vol- 

 ume, as evidenced by floating them in water. The walls of the small 

 bronchial tubes and the membrane of the larger tubes are thickened. 

 The right side of the heart is enlarged and its cavities dilated. The 

 stomach is enlarged and its walls stretched. The important change 

 found in the lungs is a condition technically called pulmonary em- 

 physema. This is of two varieties: First, what is termed vesicular 

 emphysema, which consists of an enlargement of the capacity of the 

 air cells (air vesicles) by dilation of their walls. The second form 

 is called interlobular, or interstitial, emphysema, and follows the 

 first. In this variety the air finds its way into the lung tissue be- 

 tween the air cells or the tissue between the small lobules. 



Symptoms. — Almost every experienced horseman is able to detect 

 heaves. The peculiar movement of the flanks and abdomen point out 

 the ailment at once. But in recent cases the affected animal does not 

 always exhibit the characteristic breathing unless exerted to a certain 

 extent. The cough which accompanies this disease is peculiar to it. 

 It is difficult to describe, but the sound is short, and something like a 

 grunt. When air is inspired — that is, taken in — it appears to be done 

 in the same manner as in health; it may possibly be done a little 

 quicker than natural, but not enough to attract any notice. It is when 

 the act of expiration (or expelling the air from the lungs) is per- 



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