This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
The tongue, when in a normal condition, should be freely movable, of a pink color, and the dorsum marked in the centre by a slight longitudinal depression: a velvety appearance, soft, moist and warm to the finger; the fungiform papillae circular in outline, and deeper pink than the surrounding surface; the cir-cumvallate papillae, arranged in a V-shaped row, having the form of an inverted cone, surrounded by an annular elevation. Fever causes the tongue to be frosted or coated; gastro-intestinal affections are attended by coating of the tongue, and the various appearances of this coating are of important diagnostic and therapeutic significance. Inflammation reddens the mucous membrane and makes it hot and tender, increases its moisture, changes the surface of the tongue, and causes the formation of aphthae, ulceration, and even gangrene. In aphthous stomatitis the edges of the tongue are clean and red, while its dorsum is covered with a thick white coating. In ulcerative stomatitis the tongue, besides presenting the marginal ulcers, is swollen and heavily coated with a dirty, yellowish white fur. In thrush the mucous membrane is covered with white, curd-like flakes, due to the development of the parasite oidium albicans. Prior to the appearance of the flakes the mucous membrane is purplish-red and sticky, and its secretion acid in reaction. In severe neuralgia on one side of the face, the tongue presents an unilateral furring, thickening of the mucous membrane, or enlargement of the papillae. Acute or chronic alcoholism causes a tremulous and foul tongue. Migraine causes a much furred surface of the tongue. When paralyzed, the tongue presents the appearance of a sodden mass lying in the mouth; in chorea its movements are jerking and irregular; in cerebral disease, the tongue shows a tendency to become thickly furred, and very foul, especially in apoplexy due to hemorrhage. Allowance, however, must always be made for individual peculiarities, in shape and size of the tongue, as also appearance, for effects of certain habits, such as excessive smoking or chewing tobacco, etc., taking iron, or other medicines, or for any local irritation. In some individuals the surface of the tongue presents constantly a thick fur without disturbance of organs or appetite, while on the other hand, a perfectly clean and healthy-looking tongue may be associated with severe dyspeptic symptoms or serious" alimentary trouble. The common appearances of the tongue are supposed to indicate the following conditions:
A White Coated Tongue indicates febrile disturbance.
A Brown Moist Tongue indicates digestive disorder and an overloaded stomach.
A Brown Dry Tongue indicates depressed vital power.
A Red Moist Tongue indicates feebleness, especially from exhaustive discharges.
A Red Dry Tongue indicates inflammatory fever or pyrexia.
A Red Glazed Tongue indicates debility and inability to digest food and stimulants.
A Tremulous, Moist and Flabby Tongue indicates feebleness and nervousness.
A Glazed Bluish Tongue, with loss of epithelium in patches, and in severe cases, cracks and scars, indicates tertiary syphilis.