DISEASES OF THE BRAIIT. 193 



nium. Neither is the arachnoid often affected with acute inflamma- 

 tion, 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 in- 

 flammation 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, cerehritis. Since all 

 of the conditions merge into each other and can scarcely be recognized 

 separately during the life of the animal, they may here be considered 

 together. 



ENCEPHALITIS, MENINGITIS, AND CEKEBRITIS (INFLAMMATION OF THE BRAIN AND ITS 

 MEMBRANES). 



Causes. — Exposure to extreme heat or cold, sudden and extreme 

 changes of temperature, excessive continued cerebral excitement, over- 

 feeding with nitrogenous foods, 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 

 by 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 these are followed by symptoms indicating 

 depression. Acute encephalitis may be ushered in by an increased 

 sensibility to noises, with more or less nervous excitability, contrac- 

 tion of the pupils of the eyes, and a quick, hard pulse. In very acute 

 attacks 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. Where the membranes are greatly implicated, 

 convulsions and delirium with violence may be expected, but where 

 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 or depressed with often a dila- 

 tation of the pupils, and deep, slow, stertorous breathing. The 

 H, Doc. 795, 59-2 13 



