I. Chronic Meningitis.
J. Polioencephalitis Corticalis. Inflammation of the brain cortex.
K. Polioencephalitis Superior. Inflammation of convolutions around the Sylvian fissure, palsy of the eyeball.
L. Polioencephalitis Inferior. Inflammation of the Medulla, bulbar palsy.
M. Interstitial Inflammation of the Brain. Resulting often in sclerosis.
In the lower animals, however, where we cannot avail of subjective symptoms, such fine distinctions can rarely be made in diagnosis and except in case of an uncomplicated meningitis, or a circumscribed encephalitis, which affects only a limited group of muscles like those of the eye, arm, or leg, we have to fall back upon a more general diagnosis. Again meningo-encephalitis is more common than the uncomplicated affection of the brain, or the membranes, and therefore, we shall follow Trasbot in dealing with the combined affection, and noting incidentally the distinctions that can be made in the more purely limited affections.
Causes. Mechanical Injuries. Pachymeningitis occasionally results from blows or other injuries upon the head, especially in stallions and vicious horses struck with a heavy whip or club, cattle and sheep injured in fighting, and oxen hurt by the yoke. These injuries may also affect the brain as in concussion, or by the extension of the disease into the nervous tissue. In the cranium of a stallion in the New York State Veterinary College Museum the whole of the meninges are greatly thickened by a traumatic meningitis of old date and the subjacent cerebral convolutions of the right hemisphere are deeply encroached on, flattened and absorbed over an area of 1¾ inches in the longest diameter.
Diet. Among the most common causes of encephalitis in horses is an injudicious dietary. Overfeeding with grain, but especially with grain and seeds that are rich in albuminoids deserve the first mention. The various leguminous seeds, peas, beans, tares, vetches, and the ripened leguminous fodders, clover, alfalfa, and sainfoin, are especially to be incriminated. These are usually most dangerous when in the stage of advanced ripening and yet not fully matured, evidently indicating the development of narcotic poison at this stage. Such poisons are found habitually in certain species, like the chick vetch (vicia cicera) which produces paralysis when fed to the extent of more than one-twelfth part of the ration. This danger is not, however, confined to the leguminosæ; an over abundant ration of cottonseed meal has a similar effect, and indeed this rich alimentary product has been practically discarded from pig feeding, and largely as the main constituent from the ration of dairy cows. Gluten meal, another product rich in proteids, is attended by similar dangers. But it is not alone the seeds that are rich in nitrogen that are to be dreaded, forced feeding even on the carbonaceous maize induces disorder of the digestion and brain, especially in dairy cows. Buckwheat, also, and indeed all the heating carbonaceous grains tend to similar disorders, and are especially injurious in internal ophthalmia (recurring ophthalmia) which is so closely related to brain congestion. With sound judgment and in well balanced rations, all such agents can be fed to advantage; it is only when fed exclusively or to excess as the heavy ration that they are to be feared.
Narcotics. Next must be noted those alimentary matters which are hurtful by reason of narcotic constituents. At the head of this list may be placed the lolium temulentum or intoxicating ryegrass. like the vicia sativa or cicera, the seeds of this are always poisonous, hence its significant name. Then the other ryegrasses, perennial and annual (Italian), though perfectly safe in ordinary circumstances, develop at the period of ripening a narcotic principle, which produces cerebral congestion or inflammation in whole stables of horses at a time. The lolium temulentum is poisonous to man and animals alike. Baillet and Filhol obtained from the seeds an etherial extract containing a bland oil to the amount of two fifths and a yellow extract to the extent of three-fifths. The amount of this extract derived from three ounces of the seeds often developed the most violent symptoms in the dog, while that furnished by six pounds of the seeds proved fatal to the horse. Pigs and cattle seemed to be unaffected by the agent when given by the mouth. Sheep suffered more but required large doses. Ducks and chickens were practically immune, being affected only by very large doses. Rabbits were not poisoned by the yellow etherial extract, but succumbed to a watery extract. Brydon found that lambs suffered extensively from eating the heads of the ryegrass.
Lupins on certain lands produces an icteric disorder accompanied by cerebral symptoms but the result is not the same under all conditions and it has been suspected that the symptoms were caused by cryptogams and their products. The same remark applies to the brain symptoms sometimes produced by trefoil, equisetum and other plants.