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.