Part 20

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.

A great number of =narcotic= and =narcotico-acrid= plants produce nervous symptoms indicating cerebral congestion or inflammation such as ranunculus, wild poppy, digitalis, fennel, œnanthe crocata, hellebore, veratrum, conium, yew, tobacco, box, aconite, cicuta virosa, even buckwheat at the time of flowering, vetch and flax.

Fodders affected with =cryptogams= or =bacterial ferments= are undoubtedly at times the cause of encephalitis. Veterinary records furnish many instances of wide spread attacks of stomach staggers, abdominal vertigo, and cerebro-spinal meningitis in wet seasons, when the fodders have been harvested in poor condition, or when from inundation or accidental exposure they have become permeated by cryptogams and microbes. Among comparatively recent accounts of this are those of Martin and Varnell (musty oats), Lombroso, Depre, Erbe, Pellizi, and Tireli (smuts), Bouley and Barthelemy (musty fodder), and Ray (fermented potatoes). One of the most extended local outbreaks of cerebro-spinal congestion I have seen, occurred in the pit mules of the Wilkesbarre coal mines, while fed on Canadian hay which had been soaked with rain in transit and had undergone extensive fermentation. It should be noted that there were the attendant factors of overwork, in anticipation of a strike, and a Sunday’s holiday above ground in a bright summer sunshine.

The experimental administration of moulds, smuts and microbes, have in the great majority of cases led to little or no evil result (Gamgee, Mayo, Dinwiddie, etc.) and there is a strong tendency to discredit the pathogenic action of these agents in reported outbreaks. The safer conclusion perhaps would be, to recognize the fact that they are not equally pathogenic under all conditions of their growth and administration. The oft-recurring epizootics of brain disease in connection with wide spread spoiling of the fodders in remote and recent times, probably imply that cryptogams or microbes and their products, plus some condition not yet fully understood are efficient concurrent factors. If we can discover this as yet unknown factor and demonstrate that it operates with equal power in the absence of the cryptogams and ferments, as in their presence, it will be logical to pronounce these latter as nonpathogenic under all circumstances. Until then cryptogams and bacteria must be held as probable factors.

A continuance of =high temperature= is an undoubted factor and becomes more potent, if conjoined with a close, damp, ill-aired stable.

=Violent exertion= especially in hot weather produces active congestion of the brain and occasionally merges into meningo-encephalitis. If the animal has been for sometime confined to the stable on rich aliment the condition is aggravated.

=Railroad travel= is another recognized cause.

Any considerable =change of the conditions of life= may operate in the same way. A sale and transport to a distance with change of feed, water, work, stabling and even of climate is at times a potent factor. Prietsch has seen a horse attacked three times in a single year, and on each occasion after a change of ownership and locality. Trasbot quotes an Algerian veterinarian to the effect that many of the percheron horses imported into the Mitidja are attacked by encephalo-meningitis during the extreme heats of summer.

A careful observation of cases will however show that in the majority of cases an attack comes not from one individual factor alone but from a concurrence of several operating together.

Other cases are caused by =embolisms= and =infections= from diseases localized in other parts of the body. Thus we have cerebral abscess in pyæmia, strangles and omphalitis, and cerebral congestions and inflammation in canine distemper, equine contagious pneumonia, laminitis, and angina.

Among mineral poisons, =lead= is notorious as a cause of acute cerebral disorder often leading to inflammation. Other mineral poisons like =arsenic= and =phosphorus= may lead to encephalitis symptomatic of gastro intestinal irritation, or caused by the toxic products of indigestion.

Rapidly growing =tumors=, like cholesteatomata, are liable to induce recurrent attacks of encephalitis in connection with periodic irritation.

Finally =parasites= in the cranium are sufficient causes of attacks. In the New York State Veterinary College Museum is the brain of a cat with a nematoid wound round the hypophysis. In equine subjects suffering from the strongylus armatus the larval worm or clots caused by its presence in other arteries sometimes invade the encephalic blood vessels causing disturbances of the circulation, embolism, inflammation or degeneration. (Albrecht, Von Heill). The larvæ of the œstrus has also been found in the brain substance producing inflammatory or degenerative foci (Brückmüller, Megnin, Siedamgrotzky). Their presence in the nasal sinuses at times cause encephalitis by contiguity. The cestoid worms, cœnurus in sheep and other ruminants, and cysticercus in swine, find their natural larval habitat in the brain and by their movements produce more or less congestion and inflammation. Cases of cœnurus in the horse have been described by Rousset, Frenzel, Zundel, and Schwanefeldt.

Symptoms. The symptoms of uncomplicated meningitis on the one hand and encephalitis on the other are rarely seen, the disease usually implicating more or less both brain and meninges, in a common inflammation or the symptoms of the one involving those of the other through proximity or interdependence of function. And yet in traumatic lesions of the cranial walls, the symptoms may be those of pure meningitis, and in thrombosis, embolism or parasitism of the brain, and in certain tumors they may be those of simple encephalitis. The distinction consists largely in the predominance of fever, hyperæsthesia, active delirium and convulsions in meningitis, and especially in its earlier stages; and the prominence of dullness, stupor, somnolence, muscular weakness, paralysis, anæsthesia, coma, and the clouding of special senses, with much less pronounced febrile reaction, or vascular excitement in encephalitis.

There is usually, however, a mixing of symptoms so that the benumbing or paralysis of the nervous functions alternates with periods of their exaltation, and with both conditions hyperthermia exists, though usually higher with meningitis.

The manifestations of benumbing or paresis may be continuous or interrupted, and are exhibited in stupor, coma, somnolence, lethargy, paresis or paralysis. The manifestations of excitement are not continuous but occur in paroxysms or at least exacerbations, which may show in visual or mental illusions, active, violent delirium, trembling, rigors, clonic or tonic spasms. The onset is usually abrupt, the animal passing in a few hours from apparent health, to pronounced nervous disorder. The horse seems drowsy and stupid, standing with semi-closed eyes, often drooping lower lip and ears, head pendent and resting in the manger or against the wall in front, the back arched and the limbs drawn together. When moved, it walks unsteadily and often the limbs are left out of plumb, one extending unduly forward, backward or to one side, and often crossing over its fellow. Some cannot be made to back, others back spontaneously hanging on the halter. Turning short in a circle is difficult or impossible and tends to throw the patient down. Yet some exceptional cases will turn around spontaneously to the right or left, and an animal tied to a post goes around it at the end of its halter in its effort to pass straight forward. The circling movement may be due to the irritation on the one side of the brain or to irritation of particular ganglia and nervous tracts as noticed under cerebral hyperæmia.

Appetite is usually lost, or, more properly, the animal no longer takes notice of surrounding things, not even of its food. In some cases, however, in which stupor or coma is not extreme the animal will eat a little during his quiescent intervals. In ryegrass and other dietetic poisoning, the animal may still eat and fall asleep with the month full. The digestion is impaired or suspended, the bowels costive, and fermentations with tympanies and rumbling are frequent complications. When originating from poisonous food this often contributes to these abdominal complications.

Respirations in the comatose condition are deep and slow, sometimes not more than four or five per minute. The heart usually beats strongly, often tumultuously, and the pulse varies greatly—infrequent or frequent, strong or weak, full or small. With cerebritis it is often abnormally slow.

Hyperthermia is always present to a greater or less extent, being often more marked in the more violent forms or those in which meningitis appears to predominate than in the purely cerebral forms. The temperature may vary from 101° to 106°.

The optic disc is congested.

Probably in all cases or nearly all there is a preliminary stage of excitement, in which the eye is clear, the eyelids open, the aspect alert and the whole skin affected by a marked hyperæsthesia. In some cases the symptoms of excitement are much more violent at the outset of the disease, as marked by trembling, nervous movements, pawing, pushing the head against the wall while the motions of walking or trotting are performed by the limbs, or those of plunging forward, rearing up, drawing back on the halter, etc.

But even when the disease seems to have started with stupor and coma, these paroxysms of excitement almost invariably appear at intervals as it advances. Some, however, plunged in stupor or coma at the first, remain in this condition until they end in paralysis or death, or start in convalescence.

During one of the paroxysms the trembling animal may push his head against the wall as if pulling a heavy load; at other times he will plunge with his feet in the manger and recoiling, fall to the ground, where he struggles violently in an apparent effort to rise; others rear up, pulling on the halter or breaking it and falling back over; some pull back on the halter and throw themselves down; some grind the teeth, or seize the manger, or strike blindly with the fore limbs. When seized out of doors the horse may be quite uncontrollable and refuse to return to the stable even when led by two men with double halters. In all such cases the eye has a fixed, glaring aspect which is the more pronounced when the pupils are dilated, the conjunctiva is deeply congested, of a deep, brownish red with a tinge of yellow. This is usually greatly enhanced by the bruises and extravasations caused by pushing or knocking the head against the wall. The same violence may lead to serious bruises and injuries elsewhere, even fractures of the orbital process or zigoma, of the ilium or ischium, of the poll or the base of the brain; also of the incisor teeth.

These paroxysms may be so frequent that they seem to be subject to remissions only, and not separated by complete intermissions. During the paroxysms breathing and pulsations are both greatly accelerated.

The gravity of the attack may be judged in part by the violence and frequency of the paroxysms. Yet some cases, marked by profound coma from the first, prove the most rapidly fatal, and the paroxysms of excitement and violence are not incompatible with recovery. Improvement may usually be recognized by the increased length of the intervals between the paroxysms, and by the shortening and moderation of the periods of excitement. After the paroxysms have ceased the drowsiness or stupor gradually disappears, and the hyperthermia subsides.