PART I.--INTRODUCTORY


CHAPTER I

GENERAL DISCUSSION OF DISEASE


Disease is the general term for any deviation from the normal or healthy
condition of the body. The morbid processes that result in either slight or
marked modifications of the normal condition are recognized by the
injurious changes in the structure or function of the organ, or group of
body organs involved. The increase in the secretion of urine noticeable in
horses in the late fall and winter is caused by the cool weather and the
decrease in the perspiration. If, however, the increase in the quantity of
urine secreted occurs independently of any normal cause and is accompanied
by an unthrifty and weakened condition of the animal, it would then
characterize disease. Tissues may undergo changes in order to adapt
themselves to different environments, or as a means of protecting
themselves against injuries. The coat of a horse becomes heavy and appears
rough if the animal is exposed to severe cold. A rough, staring coat is
very common in horses affected by disease. The outer layer of the skin
becomes thickened when subject to pressure or friction from the harness.
This change in structure is purely protective and normal. In disease the
deviation from normal must be more permanent in character than it is in the
examples mentioned above, and in some way prove injurious to the body
functions.