_Causes._ These may be classed as mechanical, chemical, microbian and other irritants. In the horse it is often due to the reckless administration of irritant liquids as remedies. Owing to the length of the soft palate the horse can refuse to swallow any liquid as long as he chooses, and some of the worst cases of stomatitis I have seen resulted from the retention in the mouth of caustic alkaline liquids given under the name of “_weak lye_.” Strong acids and caustic salts dissolved in too little water or other excipient, or suspended in liquids in which they cannot dissolve, or made into boluses which are crushed between the teeth are not infrequent conditions. Too hot mashes given to a hungry horse is another cause of this trouble. Fermented or decomposed food is often most irritating. Coachmen will sometimes induce it by attaching to the bit bags of spicy or irritant agents, to cause frothing and make the animal appear spirited. Fungi in fodders are among the common causes. The rust of wheat (puccinia graminis), the caries of wheat (tilletia caries), the blight (erysiphe communis), ergot (claviceps purpurea), the fungus of rape (polydesmus excitiosus) and the moulds (penicillium and puccinia) have all been noticed to coincide with stomatitis, and charged with producing it. On the other hand, at given times, one or other of these cryptogams has been present extensively in the fodder without any visible resultant stomatitis. The apparent paradox may be explained by the fact that these fungi vary greatly in the irritant or harmless nature of their products according to the conditions under which they have grown, and the stage of their development at which they were secured and preserved. Ergot notoriously differs in strength in different years, on different soils, under various degrees of sunshine, shade, cloud, fog, etc. In different States in the Mississippi valley it is not uncommon to find stomatitis in horses in winter, fed on ergoted hay, while cattle devouring the same fodder have dry gangrene of feet, tail and ears. Yet in other seasons the ergot fails to produce these lesions. Rank grown, watery vegetation, especially if it contains an excess of chlorophyll is liable to cause stomatitis. Red and white clover, trefoil, hybrid and purple clover, and alfalfa have all acted more or less in this way, though in many cases, the food has become musty or attacked by bacterial ferments. Some of the strongly aromatic plants, and those containing acrid principles (cicuta virosa, œnanthe crocata, mustard, etc.) cause buccal inflammation and salivation.