The chief _causes_ are exposure to wet and cold and especially when the subject is exhausted and the skin relaxed and covered with perspiration. In these circumstances a piercing wind, a cold drizzling rain, or a draught in the stable is particularly dangerous. Sudden alternations of temperature and especially a change to a warm stable when the general effect is aggravated by the impurity of the atmosphere and the irritant emanations from dung and urine. Damp climates are more injurious than those that are clear, dry, and bracing, and so are equally damp stables whether the moisture is due to the nature of the soil, such as a cold impervious and undrained clay, or of the building which, from its newness, may retain a dangerous amount of moisture in the plaster, or because of the hygroscopic properties of the building materials which draw moisture from the surrounding soil. It mainly attacks young horses after they have passed out of the hands of the breeder or dealer, and have been placed in new conditions of life alike as regards feeding, stabling and work. Old and ill-conditioned animals are more susceptible than the strong and vigorous, and the changes of the coat in spring and autumn prove strong predisposing causes. Nervous causes are potent in causing engorgement of the erectile tissue covering the turbinated bones, and local irritants, like septic dust, lime, ipecacuanha, pollen of certain plants, smoke, and irritating fogs may precipitate it. Iodine in large doses produces temporary catarrh. The weakness of the mucosa from a previous attack predisposes to a second. Occasionally the disease sweeps over a country, assuming the form of an _epizootic_ when it may perhaps be preferably considered as a catarrhal fever, strangles or mild type of _influenza_, _which see_. _Symptoms._ In the _milder forms_ of _coryza_ the symptoms may be almost exclusively local, consisting in redness and dryness of the membrane lining the nose and sneezing, soon followed by the bilateral discharge of a thin transparent watery liquid, succeeded by a turbid flow (epithelial cells in excess) and after two or three days by a thick, white, flocculent, puriform fluid (suppuration diapedesis). With the supervention of the purulent discharge, comes an abatement of the local inflammation and the freer the discharge the greater usually is the relief obtained and the more rapid the recovery. The eyes are usually red and watery and sometimes the eyelids are swollen. This implies the continuity of the inflammation through the lachrymo-nasal duct, and the obstruction to the flow of tears into the nose.