A great deal of experimental work has been done to determine the relations among these three parts of the taste bud. It was at one time thought that the supporting cells were modified epithelial cells and only served as a structural support for the taste cells, which were real nerve cells. According to this view, the taste cell is a neurone[6] which is directly affected by the stimulus and forms the first link in the chain of neurones connecting the surface of the body with the brain. They were thought to be analogous to the olfactory cells, which are true nerve cells. But a number of facts more recently determined tend to minimize the distinction between supporting cells and taste cells. For instance, when certain stains are employed for isolating the different structures it is found that these two sorts of cells stain alike, while the nerve fibrils within the buds stain differently from them. This is taken as good evidence that there is a difference in the composition of the taste cells and the nerve fibrils, and a likeness between the taste and the supporting cells. In fact, both types of cells are now considered to be modified epithelial cells and to be, in a sense, supporting cells. The former serve as supports for the very delicate nerve fibrils as they pass through the taste bud, and the latter, in addition to acting as supports in this way, also form the walls of the taste bud and thus protect the nerve fibrils from undue compression. According to this view, then, the nerve fibrils themselves are directly affected by the stimuli. Their knob-like endings, which are found so closely associated with the taste pore in most cases, lend support to this view. Footnote 6: Neurone is the name given to a nerve cell, and includes the cell body with its nucleus, and all of its branches. One further sort of evidence tends to show the merely secondary function of these two types of cells in the taste bud. Certain portions of the tongue, e.g., parts of the tip and sides, which are extremely sensitive to taste stimuli, have very few taste buds, or none at all. But there is a multitude of free nerve endings in these parts which are thought to function without the aid of the supporting, or taste, cells. It will be recalled that in Chapter V it was necessary to conclude that there seemed to be no absolute dependence of taste sensations upon the presence of taste buds. _The Sensory Nerves of Taste_