In horses that have the bad habit of retaining masses of half masticated food in the cheeks the growth of cryptogams is greatly enhanced and such food often becomes violently irritating.
Among other mechanical causes may be named pointed or barbed hairs or spines (barley awns, spikes, thorns, etc.) which, lodging in a gland orifice, or in a wound of the gum or mucosa, form a source of irritation or a centre for bacterial growth and abscess.
Again, irritants of animal origin must be named. These are not taken by choice, but when lodged in fodder, or in the pastures they are taken in inadvertently with the food. In this way poisonous insects, and especially hairy caterpillars, cantharides, potato bugs, etc., gain access to the mouth.
It must not be overlooked that stomatitis occurs as an extension, sympathetic affection or sequel of diseases of other organs. Gastritis is usually attended by redness and congestive tenderness of the tongue, especially of the tip and margins, and other parts of the buccal mucosa, notably the palate just back of the incisors, are often involved. In other cases it appears as a complication of pharyngitis, laryngitis, of affections of the lower air passages, of the teeth and periodontal membrane or of the salivary glands.
It appears also in a specific form in certain fevers, as in horsepox, pustulous stomatitis, aphthous fever and even in strangles. Mercurial stomatitis, rarely seen at the present time, is one of the worst forms of the disease, and like the infectious forms will be treated separately.
Lesions and Symptoms. At the outset and in the slighter forms of congestion there is merely heat and dryness of the buccal mucosa. Redness may show on the thinner and more delicate portions of the membrane, as under the tongue, on the frænum, and on the sublingual crest. But elsewhere it is hidden by the thickness of the epithelium, and the manifestations are merely those of suppressed secretion with local hyperthermia.
As the congestion is increased there is seen, even at this early stage, a slight thickening or tumefaction of the mucosa, especially on the gums, lips, the sublingual area, the orifices of the salivary glands, and the palate back of the upper incisors. On the dorsum of the tongue, the cheeks and lips, generally the lack of loose connective tissue tends to prevent the swelling.
With the advance of the inflammation the redness of the mucosa extends, at first in points and circumscribed patches, and later over the entire surface. The epithelium drying and degenerating in its surface layers forms with the mucus a sticky gummy film on the surface, which, mingling with decomposing alimentary matters gives out a heavy, offensive or even fœtid odor.
The different parts of the mouth are now tender to the touch, and this, with the fœtor and even bitterness of the bacterial products combine with the general systemic disturbance in impairing or abolishing appetite. In any case mastication becomes slow and infrequent, and morsels of food are the more likely to be retained, to aggravate the local condition by their decomposition.
The dry stage is followed by the period of hypersecretion, and in this the salivary glands take a prominent part, so that ptyalism (slobbering) becomes the most marked feature of the disease. The saliva mixed with the increasing secretion of mucus and the abundance of proliferating and shedding epithelium, escapes from the lips and falls in stringy masses in the manger and front of the stall. When there is much motion of the jaws and tongue it accumulates as a froth around the lips.