8. Give the causes and treatment of "heaves."




CHAPTER IX

DISEASES OF THE CIRCULATORY ORGANS


GENERAL DISCUSSION.--The circulatory organs are the heart, arteries, veins
and lymphatics. The _heart_ is the central organ of the circulatory system
(Fig. 23). Its function is to force the blood through the blood-vessels. It
is situated in the thoracic cavity between the lungs, and enclosed by a
special fold of the pleura, the pericardial sack. There are two kinds of
blood-vessels, arteries and veins. The _arteries_ leave the heart and carry
the blood to the many different organs of the body. The _veins_ return to
the heart and carry the blood from the body tissues. The _capillaries_ are
small blood-vessels, microscopic in size, that connect the arteries with
the veins. The arteries carry the pure blood. The opposite is true,
however, of the lesser or pulmonary system. The pulmonary artery carries
the impure blood to the lungs, and the pulmonary veins carry the pure blood
back from the lungs. The _lymphatic vessels_ carry a transparent or
slightly colored fluid and chyle from the tissues and alimentary canal.
This system of vessels empties into the venous system.

[Illustration: FIG. 23.--Photograph of model of horse's heart: auricle;
ventricle; pulmonary artery; pulmonary veins; posterior aorta; and anterior
aorta.]