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 The Sense of Taste.—The sense of taste lies chiefly in the taste buds as they are called which are filled with gustatory cells and are found in the papillæ of the tongue, principally in the circumvallate papillæ at the back of the tongue, which are few in number and arranged in a V-shape. There is also a certain power of taste in the tip and sides of the tongue but little in the upper surface or dorsum. Only five special tastes can be distinguished: bitter, sweet, acid, sour, and salt, but sometimes more than one can be distinguished at a time, as bitter and sweet. Every one can distinguish between different tastes but the power varies in different people and with different conditions. Certain tastes seem to be better distinguished in certain places, as sweet at the tip and bitter at the back of the tongue. Moreover, the sense of taste is very dependent upon the sense of smell, especially in the case of aromatic and savory substances, which one really does not taste but smell. If one held his nose and closed his eyes he would not know from the taste whether he was eating onion or apple. This leads to the habit of pinching the nose when taking nauseous medicines.

To be tasted a substance must be in solution. Friction against the tongue, lips or cheek increase the sense of taste. A temperature of 100° Fahrenheit favors taste, while both great heat and great cold impair it.

There are probably at least two nerves of taste, the lingual branch of the trifacial or fifth cranial and the gustatory branch of the glosso-pharyngeal.

Along with the sense of taste there are other senses in the mouth which play an important part, such as pressure and the sense of heat and cold, and it is often hard to distinguish them from the pure sensation of taste, which indeed is always accompanied by them.

Salivary Glands.—On either side of the mouth are three racemose glands for the secretion of the saliva, which serves to soften and lubricate the food and partially to digest starches by means of its ferment, ptyalin.