In encephalitis the affected superficial gray matter of the ganglia or convolutions, is deepened in color, usually in limited areas corresponding to the disease of the meninges. Sometimes the color becomes of a distinctly reddish tinge, and when cut into shows unusually prominent red points where the capillaries have been cut. Somewhat larger areas of blood staining indicate hæmorrhagic extravasations. The nervous substance is more or less infiltrated with liquid and softened. The nerve cells are swollen, and in process of granular degeneration and the same is true of the myelin, while the axis cylinder is uneven in its outline. Apart from the numerous minute petechial hæmorrhages there is an abundant migration of leucocytes which are found scattered in the degenerating and softened nervous tissues.
The softening of the nervous tissue may result in a pulpy material, which in the comparative absence of blood is grayish (gray softening), if abundantly infiltrated with blood is red (red softening), if older and discolored is yellow, as in an old extravasation, (yellow softening), if thick and viscous is gelatinoid softening. If the exudate becomes organized into fibrous material it is a connective tissue sclerosis or a cicatrix. If the softening exudate becomes purulent it constitutes a cerebral abscess. Cerebral abscess is especially common as secondary abscess in strangles or contagious rhino-adenitis in the horse, but may occur as the result of the presence of any pyogenic germ.
Diagnosis. While there is a certain similarity to rabies, the horse with encephalo-meningitis is distinguished by the absence of the extreme hyperæsthesia and irritability, of the persistent neighing and squealing, of the rapid alterations of the voice, hoarse and shrill, of the hallucinations, as following imaginary objects with the eyes, of the readiness to attack with teeth or heels when in any way disturbed or excited, of the disposition to get violently excited when a dog is brought near, or in the case of a stallion to show generative excitement.
From cerebral congestion it is to be distinguished by the greater severity of the paroxysms, or the deeper character of the stupor, but above all by the presence of the hyperthermia and other indications of fever.
Immobility which presents the symptoms of drowsiness, stupor and hebetude, is also unattended by fever, or anorexia, shows a healthy condition of the functions, of respiration, digestion and assimilation and a restful condition when left quiet and still.
The cerebral excitement that sometimes appears in influenza is really an encephalitis complication, but its specific cause is recognized in the local prevalence of the infectious disorder, and the inflammatory or catarrhal condition of the mucous membranes.
The diagnostic manifestations of meningitis and encephalitis respectively are given under symptoms.
Symptoms in Cattle. In cattle encephalo-meningitis supervenes on congestion, and sometimes comes on abruptly in connection with traumatic injuries, acute gastric disorder, leadpoisoning, or narcotism. The cases of cerebral parasitism are usually slow in their onset.
Upon the preliminary dullness and somnolence there supervenes excitement, manifested by loud bellowing, pushing the horns, forehead or teeth against the wall, labored often stertorous breathing, a fixed eye often with dilated pupil giving it a peculiar glaring appearance, movements of the jaws, frothing at the lips, tremors, muscular spasms, twitching, or a restless disposition to move, in a circle, in a straight line or less frequently backward. The patient seems to see nothing and is utterly regardless of obstacles. Sometimes the animal plunges violently into manger or rack, against or through the partition of his box, through fences, into ponds, pits, quarries and other dangerous places that may be accidentally in his way. The paroxysms may be intermitted by intervals of comparative calm, and tend to merge into a condition of dulled sensation, staggering, stupor, hebetude and paralysis. The congested conjunctiva and, when it can be seen, the optic disc will correspond to the cerebral congestion. These cases usually proceed to a fatal issue in a few hours. Some cases, however, make a good recovery after a few days of dullness and prostration. In cases that are connected with lead poisoning, or the toxic action of narcotics in the fodder, the attendant circumstances will assist in the diagnosis. From malignant catarrh implicating the encephalon, it may be distinguished by the absence of the catarrhal inflammation of the conjunctiva, pituita, sinuses, buccal mucous membrane, and genito-urinary passages. Also of the tendency to implication of the hair follicles and the keratogenous tissue of the frontal horns.
In the Edinburgh Veterinary Review, Dundas describes a form of alcoholism in cows caused by feeding these animals on “burnt ales” in the vicinity of distilleries. The ale is given by steeping straw in it, and the animals will also drink it freely. They often sleep soundly after such a beverage or give evidence of intoxication. The head is turned singularly to one side and slightly elevated. The pupils are widely dilated, and the eyes have a remarkably wild appearance. On being approached the animals wink rapidly and tremble. There is marked heat of head, horns, and ears. When pressed with the finger in the axilla they fall instantly and when pulled by the head they incline to turn over. The pulse is 70 to 80 per minute. Delirium and loss of coördination of the muscular movements set in, and in case of survival various forms of chronic brain disease are manifested. In one cow the violent symptoms came on with the near approach of parturition. The post mortem lesions consisted in ramified redness and punctiform blood extravasations in the pia mater and meninges. The brain substance was softened and clots of blood were found in the lateral ventricles. Congestion and extravasations were also found around the cervical myelon. (See Alcoholic Intoxication).