Page:Collier's New Encyclopedia v. 09.djvu/315

LEFT TASTE 263 TASTE stances are the surface and sides of the tongue, the roof of the mouth, and the entrance to the pharynx. The mucous m.embrane is invested by stratified squa- mous epithelium, which, over the surface of the tongue, covers little vascular pro- jections termed papillas. One can see the papillae of the sides and upper part of the tongue with the naked eye, as little sharp or rounded projections; the latter, thickly clustered at the tip and sides, may appear, if the system is out of order, as little red points like those of a strawberry. In the cat tribe the papillae are hard and curved backward into the mouth, so that the animal can use the tongue as a scraper to remove the flesh from the bones of its prey. The pointed papillaa are termed "filiform." They are essentially the same in struc- ture,. differing alone in shape and size. At the back of the tongue are some 8 or 10 papillas of quite a different nature, called "circumvallate." They are ar- ranged to form a V with its angle point- ing backward. These are hardly papillae at all, but may be looked on rather as tiny patches of mucous membrane trenched out from the surrounding parts. Into these trenches Ebner's glands se- crete a watery albuminous fluid, keeping them perpetually moist and free from foreign particles. In the epithelium lining these trenches curious little bod- ies called taste bulbs are lodged; and, as these are the parts which are probably more especially concerned in taste, they must be carefully described. Each taste bulb looks like a flask-shaped barrel or box, the walls of which are composed of flat elongated epithelial cells fitted side by side like the staves of a cask. The taste bulbs open each by a little pore into the trench, and into the deeper part a nerve enters. The cask is prob- ably for the protection of the sensory cells which it contains. These cells are much elongated, and end each in a tiny bristle which projects with those of their companion cells from the little pore into the trench, and is here moistened by the juice of Ebner's gland and whatever sapid substance may be present. The impressions which these sensory cells receive from the bristles, say by the ac- tion of a bitter like "hops," is carried by the delicate nerve which starts from the opposite end of the cell out of the taste bulb directly to the brain. Within each taste bulb are other cells, which separate and support the sensitive cells, and are similar to analogous structures seen in the sensory epithelium of the eye, and nose, and ear. While it is almost certain that these taste bulbs are organs of taste, it is not equally certain that other parts are not involved. It may be remarked that sub- stances capable of dissolving in the juices of the mouth are alone tasted. Marble, wood, flint, are devoid of taste, and so is pure starch; these are all of them quite insoluble in water. By the aid of various means we can convei't the last-named substance into a very soluble "dextrine," yet this is tasteless. Another chemical product of the starch is a sol- uble substance termed "dextrose," which has a sweet taste and is commonly termed "grape sugar." These examples will serve to illustrate the general fact that substances to be tasted must be in so- lution, though not all soluble substances are capable of giving rise to this sensa- tion. The various taste sensations are not equally produced on stimulating the whole of the gustatory area, and indeed each taste seems to have some special locality at which it is most acutely felt. If we take a piece of quassia or a hop leaf and chew it, we shall at first be un- conscious of taste, and it is only when the juice of the mouth laden with these bitter principles passes to the back of the mouth that the taste is felt at all. Our knowledge of what really takes place when an external agency affects the senses, sets up a nerve motion which travels to the brain and there induces a sensation, is very limited. When Newlands, Lothar Meyer, and Mendeleef discovered what is termed the Periodic Law in chemistry, it occurred to an English scientist to see if this law holds good for taste and smell; this was found to be the case (see "Proceedings" of the Royal Society of Edinburgh, 1885- 1886; and "Brain," 1886). Newlands found that if we arrange the elements in a series, beginning with that one which has the lowest and passing to that v/hich has the highest atomic weight, a periodic recurrence of function or prop- erty is found. There is a general resemblance in phy- sical properties between the 1st, 8th, 15th, etc., and between the 2d, 9th, 16th, etc. Those elements picked out of the series from their resemblance and perio- dic recurrence Mendeleef arranged in groups (see Atomic Theory), and found that similar compounds of these elements have similar tastes. To take an example (group 1), the chlorides of lithium, so- dium, potassium, rubidium, caesium are all salt, while the sulphates of these ele- ments are all saline bitters. It is evident that this group of elements, similar in their physical properties, can also pro- duce similar tastes, and we can correlate taste a physiological effect with some common physical quality.