excitement increase the frequency and cause the respirations to become
irregular. In disease the ratio between the heart beats and respirations
is greatly disturbed, and the character of the respiratory sounds and
movements may be greatly changed (Fig. 4).

[Illustration: FIG. 4.--Auscultation of the lungs can be practised to an
advantage over the outlined portion of the chest wall, only.]

Severe exercise and diseased conditions of the lungs cause the animal to
breathe rapidly and bring into use all of the respiratory muscles. Such
forced or labored breathing is a common symptom in serious lung diseases,
"bloat" in cattle, or any condition that may cause dyspnoea. Horses
affected with "heaves" show a double contraction of the muscles in the
region of the flank during expiration. In spasm of the diaphragm or
"thumps" the expiration appears to be a short, jerking movement of the
flank. In the abdominal form of respiration the movements of the walls of
the chest are limited. This occurs in pleurisy. In the thoracic form of
respiration the abdominal wall is held rigid and the movement of the chest
walls make up for the deficiency. This latter condition occurs in
peritonitis.

_A cough_ is caused by irritation of the membrane lining the air passages.
The character of the cough may vary according to the nature of the disease.
We may speak of a moist cough when the secretions in the air passages are
more or less abundant. A dry cough occurs when the lining membrane of the
air passages is dry and inflamed. This may occur in the early stage of the
inflammation, or as a result of irritation from dust or irritating gases.
Chronic cough occurs when the disease is of long duration or chronic. In
pleurisy the cough may be short and painful, and in broken wind, deep and
suppressed. In parasitic diseases of the air passages and lungs, the