Granting that a dynamic theory as outlined above, with possible modifications to meet new discoveries, is correct, still another question requires an answer. In the visual organ affected by ether vibrations of different rates every theory assumes certain parts of the mechanism sensitized especially to certain vibration rates. To take the theory of Hering, for example, there are three photochemical substances, one decomposed by a relatively slow vibration rate, another by a more rapid vibration rate, and so on. And in the auditory mechanism there is the _basilar membrane_, capable of vibration in parts in sympathy with different rates of vibration of the air. The answer to this question concerning the taste sense is peculiarly difficult, in that it is impossible to stimulate individual taste buds, and even difficult to stimulate a single papilla, which may contain many buds. And then it must be further borne in mind that each bud contains many nerve endings, so that what is stimulated in experimental work is really a very complex portion of the sense organ. As mentioned in another connection, certain papillæ when stimulated with various substances respond to but one, e.g., sweet, sour, bitter, or salt, while others respond to two or three stimuli. Further, it is well known that certain portions of the tongue when stimulated produce a predominance of certain kinds of taste sensations. On the other hand, an examination of the taste buds or of the nerve endings within the taste buds shows no differences among them. Still, in this respect taste does not differ from sight. The cones of the retina, which are sensory ends of vision, show no differences in structure, and it is generally believed that all of the elementary sensations can be produced by the stimulation of one single cone. If it be true that the nerve fibrils in the taste buds themselves receive the stimulus, then any specific characteristics of the receiving mechanism would have to be looked for in these nerve endings. Oehrwall has accounted for the facts of the specific sensitivity of different parts of the tongue and of different individual papillæ mentioned above by the assumption that each taste bud has a specific function and that certain papillæ of the tongue have buds all of one sort, other of two sorts, and so on. Nagel prefers to modify this view to the extent that each taste bud is capable of arousing every elementary sensation, but is adapted to respond best and easiest to a certain specific stimulus with a certain elementary sensation. This view is analogous to that of the visual photochemical substances which, according to the Helmholtz theory, were each sensitive to all wave lengths of light, but not equally.