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.
Even after recovery from the acute or violent symptoms there is liable to remain some aberration or perversion of function, due to the persistence of some encephalic or meningeal lesion. The general hebetude known as immobility may bespeak dropsy of the ventricles, pressure of a tumor or clot, or degeneration of ganglionic centres. Diseases of the eyes (amaurosis, glaucoma, cataract), or of the ear (deafness, disease of the internal or middle ear) are less frequent results.
The supervention of general or facial paralysis or of hemiplegia during the active progress of the malady, is an extremely unfavorable symptom.
Duration. A fatal result may take place at any time by self inflicted injuries (dashing the head against a wall, or falling backward and striking the head on a solid body). Apart from this, death may come within twenty-four or thirty-six hours. If the animal survives two to seven days recovery is more probable. Hering records a case of recovery after five weeks illness. Hot weather hastens a fatal result, while cool, cloudy weather is favorable.
Prognosis. Under rational treatment about one-fourth recover. One-half of the victims make a partial recovery but remain in a condition of dementia or hebetude, blindness, deafness, local or general paralysis which renders them more or less useless. Not more than one-fifth or at most one-fourth of all cases recover. Even in these there is left an increased predisposition to recurrence. It is noted by Trasbot that the mortality is higher in highbred, nervous, irritable animals, which show a tendency to greater frequency, force and duration of the paroxysms of excitement. When decubitus is constant, death may take place from septic poisoning starting from bed sores, and gangrenous sloughing. In other cases there is fatal starvation from inability to eat.
Lesions. In pachymeningitis due to mechanical injury there is usually cutaneous and subcutaneous, blood extravasation, and there may be fracture of the cranial bones. The dura mater is dark red, hyperæmic, thickened, covered with exudation and small blood clots mixed with pus cells, and has contracted strong adhesions to the cranial bone. Bony spicula may project into the fibrous neoplasm.
Leptomeningitis usually coexists from extension of the inflammation into the adjacent arachnoid and pia mater. There is then a reddish serous effusion into the arachnoid and beneath it, and the substance of both membranes is thickened by exudate, and discolored by congestion and minute hæmorrhages. Whenever the pia mater is thus inflamed, the superficial layer of the brain is implicated, œdematous, soft and doughy. The extension is also made into the ventricles and a serous effusion takes place often to two, three or more times the normal amount (82 grammes Schütz). The choroid plexus forms a yellowish gelatinoid mass, and the ganglia (corpora striata, optic thalamus, etc.), are flattened.