The term catarrh is generally used to describe an inflammatory condition of the lining membrane of the upper portion of the air-passages, commonly spoken of as "a cold", the special feature of which is a discharge of varied character from the nostrils, and sometimes the eyes also.
The popular term - cold, or a cold - correctly points to the origin of many cases of this disorder, but it should be understood that there are other causes of catarrh with which cold has no concern. For the most part it results from lengthened exposure to inclement weather under conditions of exhaustion and inadequate food, sudden change from an overheated and usually badly ventilated stable to the outer cold, and it is the general experience among horsemen that the opposite conditions to the latter frequently cause it. It would seem paradoxical that an animal should take cold on coming from a cold atmosphere to a warm one, and from nakedness to clothing and comforts. The explanation is probably to be found in the unwholesome and irritating nature of the stable atmosphere upon the sensitive membranes of the air-passages. A horse requires a very large amount of air space, and the inadequate amount usually allowed is only tolerated when he has become acclimatized to close quarters. The advantages of pure air as a curative agent, when catarrh is established, are so well recognized among horse-dealers that some adopt the heroic though imprudent course of turning them out in a field. When the skin of a weak perspiring horse is suddenly exposed to a cold wind, the surface circulation receives a check of which the cold is a reaction or local manifestation. The animal's condition at the time of exposure would appear to have much to do with his susceptibility in this respect; indifferent health and fatigue are unquestionably predisposing conditions. The horse in hard condition, sweating but not exhausted, will bear a cold shower-bath without taking cold, but his vital powers are sufficiently great to produce a healthy reaction.