THE so-called higher senses are usually differentiated from the lower on the basis of their greater intellectual value. The sense of taste is one of the lower, as compared with vision and hearing, which are of the higher group. Not only in the purpose which they serve, but also in the character of their mechanism, do the senses differ. The sense of taste differs from the sense of sight in at least three respects. First, it is a mechanism not given over exclusively to the taste function, but serves other functions as well. The visual mechanism, for instance, is very highly specialized. It consists of an elaborate mechanical device,—extrinsic and intrinsic muscles, lens, iris, etc.,—which serves to prepare the physical stimulus to act upon the real receptor portion of the sense organ, the retina. None of these parts of the eye serve any other purpose than that of vision. In the case of the taste mechanism, on the other hand, only the receptor[5] portion of the mechanism is concerned exclusively in the taste function. The tongue, usually considered the most important part of the taste organ, with its great variety of movements, is a very necessary part of the speech mechanism. The salivary glands, which by their secretions put the substances entering the mouth into such condition that they may act upon the receptor mechanism, are of vital importance for the process of digestion. The small receptors imbedded within the coverings of the tongue and the linings of the mouth cavity may be considered as the only structures which perform exclusively a taste function. Footnote 5: A receptor is the part of the sense organ in which the transformation from a physical stimulus to a nerve impulse occurs. Secondly, it is not easy to determine the limits of distribution of the receptor organs of taste, as one can do in the case of the eye, with its clearly defined retina, or the ear, with its organ of Corti, or even the nose, with its regio olfactoria (patch of mucous membrane). That is, there is no one organ with its attachments which can be called the taste organ. Consequently, one does not find any general agreement as to what structures ought to be included in the taste mechanism. For instance, it is well known that the taste function is not limited to the tongue, and that the whole mouth cavity is a more or less important part of the taste mechanism. Certain investigators are not willing to circumscribe the taste organ within such narrow limits, but extend it to the larynx, the vocal cords, and some have even gone so far as to include the membranes of the nasal cavity.