nes (Encephalitis, Meningitis,
Cerebritis).

Inflammation may attack these membranes singly, or any one of the
anatomical divisions of the nerve matter, or it may invade the whole at
once. Practical experience, however, teaches us that primary
inflammation of the dura mater is of rare occurrence, except in direct
mechanical injuries to the head or diseases of the bones of the cranium.
Neither is the arachnoid often affected with acute inflammation, except
as a secondary result. The pia mater is most commonly the seat of
inflammation, acute and subacute, but from its intimate relation with
the surface of the brain the latter very soon becomes involved in the
morbid changes. Practically, we can not separate inflammation of the pia
mater from that of the brain proper. Inflammation may, however, exist in
the center of the great nerve masses--the cerebrum, cerebellum, pons
Varolii, or medulla at the base of the brain--without involving the
surface. When, therefore, inflammation invades the brain and its
enveloping membranes it is properly called encephalitis; when the
membranes alone are affected it is called meningitis, or the brain
substance alone cerebritis. Since all the conditions merge into one
another and can scarcely be recognized separately during the life of the
animal, they may here be considered together.

_Causes._--Exposure to extreme heat or cold, sudden and extreme changes
of temperature, excessive continued cerebral excitement, too much
nitrogenous feed, direct injuries to the brain, such as concussion, or
from fracture of the cranium, overexertion, sometimes as sequelae to
influenza, pyemia, poisons having a direct influence upon the encephalic
mass, extension of inflammation from neighboring structures, food
poisoning, tumors, parasites, metastatic abscesses, etc.

_Symptoms._--The diseases here grouped together are accompanied with a
variety of symptoms, almost none of which, however, are associated so
definitely with a special pathological process as to point unmistakably
to a given lesion. Usually the first symptoms indicate mental
excitement, and are followed by symptoms indicating depression. Acute
encephalitis may be ushered in by an increased sensibility to noises,
with more or less nervous excitability, contraction of the pupils of the
eyes, and a quick, hard pulse. In very acute attacks these symptoms,
however, are not always noted. This condition will soon be followed by
muscular twitchings, c