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82 ENOS WALTER. 
While the horse is quiet he will show it very little at 
times, but at other times, owing to the asthmatic character of 
the disease, he may heave much even while perfectly quiet. 
Even if he does not show it while quiet, he will be found in¬ 
capable of much exertion without exhibiting more or less 
difficulty in breathing. Thus he is never entirely free from 
the disease as he would be were it uncomplicated asthma ; nor 
is the disease equally severe at all times, as it would be if em¬ 
physema alone were the cause. 
The causes of broken-wind in a horse are primarily the 
causes of the asthma and emphysema. How asthma may 
cause emphysema has already been explained. Emphysema 
may also be caused by the occlusion of some of the bronchial 
tubes as a result of bronchitis, as the cells at the end of the 
open tubes have to dilate more as the chest expands, to make 
up for the non-dilatation of the cells at the ends of the oc¬ 
cluded tubes. This over-distention of part of the air-cells 
often causes rupture of their walls, and the condition known 
as vesicular emphysema is the result. 
The causes of asthma have also been touched upon. The 
most common causes of the disease as it occurs in the horse 
are, I think, heredity and indigestion. 
That the children of asthmatic people have a decided pre¬ 
disposition to the disease is proven by statistics, as is also the 
fact that asthmatics are in the majority of cases also dyspep¬ 
tics. I have no statistics to show this to be the case with 
horses, but I believe it will be found the same with horses as 
with men. Robertson in his “ Equine Practice” says, “ It is gen¬ 
erally admitted by horsemen that broken-wind is hereditary.” 
It is believed that indigestion causes asthma from the ef¬ 
fect it has in rendering the pneumogastric nerve irritable, or 
over-sensitive. Prof. Williams says heaves is a symptom of 
indigestion and classes it with dietetic diseases. 
The effect of both asthma and emphysema is to reduce the 
capacity of the lungs for supplying oxygen to the blood, and 
rendering it a difficult task for them to supply it in requisite 
amount except when the animal is quiet and needs but a small 
quantity. The lack of oxygen Jin the blood stimulates the 
