DISEASES OF THE NERVOUS SYSTEM. 213 
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. Inflam- 
mation 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, inflamma-. 
tion 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 concus- 
sion, or from fracture of the cranium, overexertion, sometimes as 
sequelee 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 asso- 
ciated 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 depres- 
sion. Acute encephalitis may be ushered in by an increased sensi- 
bility to noises, with more or less nervous excitability, contraction of 
the pupils of the eyes, and a quick, hard pulse. In very acute at- 
tacks these symptoms, however, are not always noted. This condi- 
tion will soon be followed by muscular twitchings, convulsive or 
spasmodic movements, eyes wide open with shortness of sight. The 
animal becomes afraid to have his head handled. Convulsions and 
delirium will develop, with inability of muscular control, or stupor 
and coma may supervene. When the membranes are greatly impli- 
cated, convulsions and delirium with violence may be expected, but if 
the brain substances are principally affected stupor and coma will be 
the prominent symptoms. In the former condition the pulse will be 
quick and hard; in the latter, soft and depressed, with often a dilata- 
tion of the pupils, and deep, slow, stertorous breathing. The symp- 
toms may follow one another in rapid succession, and the disease 
approach a fatal termination within 12 hours. In subacute at- 
tacks the symptoms are better defined, and the animal seldom dies 
before the third day. Within three or four days gradual improve- 
ment may become manifest, or cerebral softening: with partial paral- 
