This is a filthy, fetid disease of the frog. By many veterinary writers it is attributed entirely to damp stables, general nasty condition of stall, yard, etc. Mayhew ingenuously remarks, in addition, that it is usually found in animals that "step short or go groggily," and that the hoof is "hot and hard." Youatt comes to the point at once in saying that it is the effect of contraction, and, when established, is also a cause of further contraction. It is manifest in a putrid discharge from the frog. The matter is secreted by the inner or sensible frog, excited to this morbid condition by pressure of contraction. Its cure is simple and easy if the cause is removed. A wash of brine, or chloride of zinc, three grains to the ounce of water, is generally used to correct the foulness. CHAPTER VII. BENT KNEES INTERFERENCE, AND SPEEDY CUT. The knee of a horse is a most complicated and beautiful mechanical arrangement, singularly exempt from strain or disease in any form. Bony enlargement, inflammation of the ligaments, do not attack it. The ravage of the shoeing-smith--the horse's direst enemy--seems to be exhausted upon the feet and the sympathetic pasterns; the concussion of iron and pavement, uncushioned by the frog, will destroy the lower system of joints before the knee can be shaken. Notwithstanding this perfection and strength, many horses bend the knee, and stand, or travel with it bent, until the flexor muscles shrink from lack of use. This "over in the knees" condition is invariably caused by imperfect use of the feet. The effect of heel-calks and their accompaniment of corns, making a sore in each heel, is often indicated by the horse to his regardless owner by bending his knee. The owner asks the smith why he does it, and the smith, who never fails to give a reason, says he has always noticed that horse had "weak knees." We know of a shoer in Worcester County, Massachusetts, who has a wide local reputation for "doctoring" weak knees. He holds that the muscles of the leg in such cases are _too short_, and have to be lengthened with thick iron heels and calks. It is a favorite theory of this class of shoers that they are able to correct the errors of Providence in the horse's construction, and piece him out with heel-calks and bar-shoes! INTERFERING AND SPEEDY CUT. If horses were not shod, they would not interfere; it therefore follows that shoeing is the cause of this defect. A contracted hoof, pain from corns, or any inflammation causes a horse to seek a new bearing. In doing this he strikes himself. Blacksmiths make "interfering shoes," welding side-pieces and superfluous calks upon their clumsy contrivances, and sometimes succeed in preventing the symptom, but they never remove the cause. Few horses with natural feet, good circulation, and shod with a light shoe, will ever interfere. In all such cases, take off the heavy shoe, cure the contraction, get an even bearing, and let nature have at least a momentary chance.