sanitary conditions present. The principal factor in stable ventilation is
the force of the wind. In cold weather it is very difficult to properly
ventilate a crowded stable without too much loss of animal heat and
creating draughts.

For practical purposes, the _need of ventilation_ in a stable can be
determined by the odor of the air, the amount of moisture present and the
temperature. It is impossible to keep the air within the stable as pure as
the atmosphere outside.

All dangers from injury by breathing impure air, or by draughts can be
eliminated by proper stable construction, attention to the ventilation and
keeping the quarters clean.

[Illustration: FIG. 22.--A case of catarrhal cold.]

CATARRH (COLD IN THE HEAD).--Catarrh is an inflammation of the mucous
membrane lining the nasal cavities that usually extends to the membrane
lining of the sinuses of the head. It may be acute or chronic. The
inflammation very often extends to the pharynx and larynx. Cold in the head
is more common in the horse than in any of the other animals (Fig. 22).

_The most common causes_ of "colds" are standing or lying in a draught,
becoming wet, and exposure to the cold. "Colds" are common during cold,
changeable weather. Horses that are accustomed to warm stables, are very
apt to take "cold" if changed to a cold stable and not protected with a
blanket. Most animals are not affected by the cold weather if given dry
quarters and a dry bed. Irritation to the mucous membrane by dust, gases
and germs is a common cause. Influenza and colt distemper are characterized
by an inflammation of the respiratory mucous membranes. In the horse,