This section is from the book "The Farmers Ready Reference Or Hand Book Of Diseases Of Horses And Cattle", by S. C. Orr. . Also available from Amazon: The Farmer's Ready Reference;.
As these two diseases are of exactly the same nature only differently located, they will be treated under the same heading. When the disease affects the withers it is fistula, or "fistulous withers;" and when situated on the top of the head it is known as poll evil. The disease has always been attributed to a bruise or local injury; but, after an extensive and varied experience in treating it, the writer is of the opinion that there is some parasitic agent connected with it, and he is glad to learn lately that there are others who concur in the same opinion.
Symptoms. - In either location the disease may begin with a stiffness of the part affected without any apparent swelling. The horse may be dumpish and off his feed for a few days and then seem all right for some time before the swelling appears. Finally the parts are swollen, hard at first, but after a time growing soft and filled with pus. It may remain swollen a year before it breaks, or it may break at any time. Sometimes the tumor grows very large.
Treatment. - If taken before the formation of pus, repeated blistering with biniodide of mercury, one part, to lard, six parts, and the administration internally of one to two drachms of iodide of potassium twice a day, may ward it off. But if pus forms, the tumor should be split open on both sides, parallel with the mane When the bleeding has ceased, fill the cavities full of lumps of sulphate of copper; grease the hair below it and let it alone for a week, when the dead tissue can be removed. This burning out should be repeated until the sore becomes healthy, when an outlet for pus should be made at the bottom, and the sore dressed once a day with chloride of zinc, two drachms; water, one pint. The iodide of potassium should also be given the same as when the sore is not open. Many cases require long and skillful treatment and some are incurable.