At the same time it is only logical to conclude that any morbid condition of the cerebral circulation or of the brain or membranes which leads to a corresponding amount of ventricular effusion, or atrophy or destruction of the nerve centres already designated, will produce the symptoms characteristic of this disease. Thus the different forms of meningitis, traumatic injuries to the cranium, chronic encephalitis, cerebral softening or degeneration, sclerosis, neoplasms of all kinds affecting the brain (cysts, cholesteatoma, psammoma, melanoma, etc.), and parasites may occasion this disease.
Prognosis. The disease is essentially incurable. It may last for years with little change except the winter improvement, but it rarely subsides permanently. It is only in those cases in which the symptoms have been determined by a transient or removable cause, as a moderate exudation or a parasite with a short term of life that a favorable result may be looked for. Usually the improvements seen in cool seasons or stables, under good hygiene, are not recoveries but temporary amelioration only.
Symptoms in other animals. Corresponding conditions produce similar symptoms in cattle, sheep, swine and dogs, but the disease receives less attention in these animals because they are not called on for steady work. The animals are lazy, dull, insensible to excitement, stupid, show a lack of muscular power and control, stagger or move disorderly and show tympanies or other indications of indigestion.
Treatment. Majendie and others had a few apparent recoveries after violent counter-irritation over the spinal cord (cervical and dorsal). Coculet and Lafosse claimed recoveries from the prolonged use of nux vomica in large doses (up to 5 drachms). Hayne attempted evacuation of the fluid by puncture through the perforated plate of the ethmoid bone, but had evil results from the ensuing hæmorrhage and encephalitis. Aseptic puncture through the plate of the frontal bone would be much more promising. Klemm suggested hydrochlorate of pilocarpin (15 grains), and this would promise better than any other measure to induce absorption of the liquid. The fatal drawback to this as to other measures is that it is not applied until the slow, steady pressure has caused such extensive cerebral atrophy that, even if the liquid could be removed and its reproduction prevented, the lost functions can never be restored. If the disease could be diagnosed and treated before this change of structure had taken place, the hope of recovery would be much better founded. Even in cases which make a temporary recovery during cold weather one would be warranted in using active derivatives toward the bowels and kidneys, also pilocarpin, counter-irritation to the spine and even tapping of the ventricles.
Legal Aspect of Chronic Hydrocephalus.
To claim relief in case a horse affected in this way is sold as sound, the seller must be notified at an early date. In the different countries of Europe a limit is set after which such notification will have no legal value. The seller must be notified, in France in 9 days, in Saxony in 15 days, in Bavaria, Wurtenberg and Baden in 21 days, in Hesse and Prussia in 28 days, and in Austria in 30 days.
Diagnosis. The veterinarian called to act as expert in such cases must examine the suspected animal along the different lines in which the cerebral aberration is manifested in the disease. He will see the animal standing quietly in the stall apart from all sources of excitement. See if there is a defect in the breadth of the cranium, or a deflection backward of this region from the straight line of the front of the face, together with a heavy clumsy head. Is the head pendent, resting on the manger, with dull eye, drooping lids, lack of expression, loose hanging lower lip? Does he hold morsels unchewed projecting from the mouth or over the tongue, or in the cheek? Does he plunge both mouth and nose in the water to drink, and masticate meanwhile? Are his legs found crossed or in abnormal positions, and if put in such positions, does he fail to rectify them at once? Is the head left in an abnormal flexed, depressed or lateral position if placed in it? Does the subject find it difficult or impossible to back? Does he pay the customary attention to the going or coming of other horses, to feeding, etc.?
If no distinct symptoms are found he should then be examined under other conditions. In taking out of the stable how does he turn in the stall or back out of it, and in what way does he approach the door, clumsily or with difficulty? When moved in a circle, does he sway or stagger? Can he back when mounted or attached to a heavy carriage? Can he execute all these movements satisfactorily after the respiration and circulation have been excited by walking, trotting or galloping in hand or otherwise? In case of difficulty in backing, in the absence of the other diagnostic symptoms, he must see that this does not arise from other causes. Some untrained horses have not been taught to back and cannot be made to do so at once. Some refuse to back from indocility or stubbornness, but can perform the act if induced in other ways, as in having a narrow stall. Sometimes a sore mouth, from a hard bit may make a horse nervous and obstinate so that he will seek to escape in any other way rather than by backing under steady pressure of the bit. Sometimes he will back all right under a halter. In all such cases of simple obstinacy or fear of pain, the absence of the other symptoms is strongly suggestive. If the horse has a well-developed cranium, a full bright, alert eye, firmness of lips, intelligent expression, readiness to appreciate and respond to all noises, words, touches or other causes of excitement, plenty of fire and spirit, and an absence of any apathy, dulness, awkwardness of movement or position of the limbs, or of any other sign of failing nervous power he may be considered free from this affection, even if he refuses to back in a docile manner. In other cases there is a distinct physical incapacity quite apart from any brain disorder. Sprains or anchylosis of the back or loins or anchylosis or painful arthritis of the hocks, may hinder backing.
The diagnosis from encephalitis and other inflammatory affections associated with stupor, rests on the absence of hyperthermia, of the congestion of the orbital and nasal mucosæ, of the heat of the head and of the paroxysmal attacks of excitement which characterize these diseases.