, the disease
causing the enlargement is chronic.

The manner in which the horse coughs is of importance in diagnosis. The
cough is a forced expiration, following immediately upon a forcible
separation of the vocal cords. The purpose of the cough is to remove
some irritant substance from the respiratory passages, and it occurs
when irritant gases, such as smoke, ammonia, sulphur vapor, or dust,
have been inhaled. It occurs from inhalation of cold air if the
respiratory passages are sensitive from disease. In laryngitis,
bronchitis, and pneumonia, cough is very easily excited and occurs
merely from accumulation of mucus and inflammatory product upon the
irritated respiratory mucous membrane. If one wishes to determine the
character of the cough, it can easily be excited by pressing upon the
larynx with the thumb and finger. The larynx should be pressed from side
to side and the pressure removed the moment the horse commences to
cough. A painful cough occurs in pleurisy, also in laryngitis,
bronchitis, and bronchial pneumonia. Pain is shown by the effort the
animal exerts to repress the cough. The cough is not painful, as a rule,
in the chronic diseases of the respiratory tract. The force of the cough
is considerable when it is not especially painful and when the lungs are
not seriously involved. When the lungs are so diseased that they can not
be filled with a large volume of air, and in heaves, the cough is weak,
as it is also in weak, debilitated animals. If mucus or pus is coughed
out, or if the cough is accompanied by a gurgling sound, it is said to
be moist; it is dry when these characteristics are not present--that is,
when the air in passing out passes over surface not loaded with
secretion.

In the examination of the chest we resort to percussion and
auscultation. When a cask or other structure containing air is tapped
upon, or percussed, a hollow sound is given forth. If the cask contains
fluid, the sound is of a dull and of quite a different character.
Similarly, the amount of air contained in the lungs can be estimated by
tapping upon, or percussing, the walls of the chest. Percussion is
practiced with the fingers alone or with the aid of a special percussion
hammer and an object to strike upon known as a pleximeter. If the
fingers are used, the middle finger of the left hand should be pressed
firmly against the side of the horse and should be struck with the ends
of the fingers of the right hand bent at a r