The foregoing facts concerning the phenomena of mixture, fusion, antagonism, contrast, and after sensation show at once the impossibility, in our present state of knowledge, of arranging the taste qualities in any such systematic scheme as is represented by the color pyramid and the tonal scale in the cases of vision and hearing. It by no means follows, however, that such orderly arrangements have not been attempted. [Illustration: Fig. 1.] Kiesow, one of the most famous students of the sense of taste, proposed that a circle with a vertical and a horizontal diameter indicated would best represent the various relations between the taste qualities. At top and bottom would stand salt and sweet; to left and right, bitter and sour. Along the horizontal diameter would be placed the mixtures of bitter and sour, and along the vertical diameter would range the various results of mixing salt and sweet. The mixtures of salt-sour, sweet-sour, bitter-sweet, and bitter-salt would stand in their appropriate places about the circumference or periphery of the circle. Wundt tentatively adopts a similar scheme when he says: “The system of taste sensations is, accordingly, in all probability to be regarded as a _two-dimensional_ continuity, which may be geometrically represented by a rectangular surface at the angles of which the four primary qualities are placed, the various mixed qualities being placed along the side and on the inner surface.” To such suggestions, however, Kuelpe objects that: “There is no indication of a continuous transition between the four qualities which tastes appear to present, as there is between the qualities of tone sensations. They form, not a one-dimensional manifold, but a discrete system of unknown relations.” Titchener, one of the most careful students of sense experience, is less emphatic, but he “doubts whether, in the present state of our knowledge, this idea (that of Wundt) can be accepted.” He doubts “whether the sweet-sour of lemonade stands to its originals as blue-green stands to blue and green, or as orange to red and yellow; and also whether bitter should lie in the same plane with the other three taste qualities. We must suspend judgment; in the meantime, Kiesow’s figure provides us with a working hypothesis.” Ladd and Woodworth align themselves with Kuelpe and conclude that, “there is no clear indication that the tastes can be arranged in a linear scale, as the primary colors are, nor that any taste stands to any other definitely in the relation of opposite or complementary. On the whole it appears as if the four tastes were rather isolated from each other, each representing almost an independent sense.” ------------------------------------------------------------------------ CHAPTER III THE SENSITIVENESS OF TASTE _Various Measures of Sensitiveness_