season,
grass and green-blade fodder are the best diet.

THE LUNGS.

The lungs (see Pl. VII) are the essential organs of respiration. They
consist of two (right and left) spongy masses, commonly called the
"lights," situated entirely within the thoracic cavity. On account of
the space taken up by the heart, the left lung is the smaller.
Externally, they are completely covered by the pleura. The structure of
the lung consists of a light, soft, but very strong and remarkably
elastic tissue, which can be torn only with difficulty. Each lung is
divided into a certain number of lobes, which are subdivided into
numberless lobules (little lobes). A little bronchial tube terminates in
every one of these lobules. The little tube then divides into minute
branches which open into the air cells (pulmonary vesicles) of the
lungs. The air cells are little sacs having a diameter varying from
one-seventieth to one two-hundredth of an inch; they have but one
opening, the communication with the branches of the little bronchial
tubes. Small blood vessels ramify in the walls of the air cells. The air
cells are the consummation of the intricate structures forming the
respiratory apparatus. They are of prime importance, all the rest being
complementary. It is here that the exchange of gases takes place. As
before stated, the walls of the cells are very thin; so, also, are the
walls of the blood vessels. Through these walls escapes from the blood
the carbonic acid gas that has been absorbed by the blood in its
circulation through the different parts of the body; through these walls
also the oxygen gas, which is the life-giving element of the atmosphere,
is absorbed by the blood from the air in the air cells.

CONGESTION OF THE LUNGS.

Congestion is essentially an excess of blood in the vessels of the parts
affected. Congestion of the lungs in the horse, when it exists as an
independent affection, is generally caused by overexertion when the
animal is not in a fit condition to undergo more than moderate exercise.
Very often what is recognized as congestion of the lungs is but a
symptom of exhaustion or dilatation of the heart.

The methods practiced by the trainers of running and trotting horses
will give an idea of what is termed "putting a horse in condition" to
stand severe exertion. The animal at first gets walking exercises, then
after some time he is made to go faster and farther each day; the amount
of work is daily increased