e 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 volume, 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 emphysema. 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 between 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. In recent cases, however, 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 performed that
the great change in the breathing is perceptible. It must be remembered
that the lungs have lost much of their elasticity, and in consequence of
their power of contracting on account of the degeneration of the walls
of the air cells, and also on account of the paralysis of muscular
tissue before mentioned. The air passes into them freely, but the power
to expel it is lost to a great extent by the lungs; therefore the
abdominal muscles are brought