1. Does the sapid substance affect the taste-bud cells, or only the nerve fibrils that twine around these cells? 2. If it affects these cells, does it affect the gustatory cells only, or both these and the supporting cells? 3. Does the sapid substance really enter the taste bud at all, or only affect the ends of the cells which form the so-called entrance to the bud? 4. Regardless of what portion of the taste bud is affected by the stimulus, what is the character of the effect produced? Is it mere contact or mechanical stimulation, or is it a chemical process which is set up? 5. Must different types of receiving structures, of whatever form they may be, be assumed for each type of elementary taste sensation? The structural relations among the parts of the taste bud were discussed in the chapter on Sensory Elements. There it was concluded that the analogy between the sense of taste and that of certain of the other senses, especially sight and smell, is not so close as it has seemed to be. It will be recalled that in these sensory mechanisms there are modified nerve structures, rods and cones in the eye, and the olfactory cells in the nose, which are affected directly by the stimuli, and in which a transformation of the stimulus takes place, with the resultant nerve impulse. This transformation accompanies a chemical change within these structures, hence vision and smell are called chemical senses. In the taste mechanism, also considered a chemical sense, it was natural to see in the gustatory cells of the taste bud structures with functions similar to that of the rods, cones, and olfactory cells. But the analogy between these types of structures breaks down because the gustatory cells do not have the characteristics of nerve tissue, as revealed especially by the use of differential stains. In fact, as has been said above, there seems to be no fundamental difference between supporting and taste cells. Two further facts seem to indicate that the supporting and gustatory cells take no primary part in the taste function. First, there is no more intimate connection between these cells and the nerve fibrils than that of contact, and the contact seems only incidental to the supporting function. The endings of the nerve fibrils are free from the cells. And, second, those free nerve endings in the anterior portion of the tongue seem to arouse taste sensations without the intervention of any structures resembling the taste buds or their cells. Thus, the evidence to date leads to the conclusion that the nerve fibrils alone are the parts affected by the taste stimulus.