that of a ship, which often causes nausea in those unaccustomed to the sea. Certain conditions of the blood flowing through the nerve centres also causes nausea, as when emetics are injected into the blood.

Giddiness, which consists of a feeling of inability to keep the normal balance, is often produced in connection with the last by irregular movements, but more surely by a rotatory motion of the body. Other afferent influences may give rise to it, viz., from the stomach, in some cases of irritation; from the eye, when we look from a height; from the semicircular canals of the ear by rotation of the body; and also from conditions of the blood, as in alcoholic toxæmia.

Shivering is the result of a peculiar nervous effect produced by afferent influences of an unpleasant kind; the sudden application of cold to the skin, a revolting sight, a shrill noise, or an intensely nasty taste-all excite a nervous condition which makes us shiver.

Titillation follows light stimulation of certain parts of the cutaneous surfaces. It is a peculiar general sensation, in moderation not disagreeable, and usually accompanied by a tendency to meaningless laughter and other-reflex movements.

CHAPTER XXXI.

TASTE AND SMELL.

SENSE OF TASTE.

Next to the sense of touch, which is unevenly distributed over the whole cutaneous surface, taste is anatomically the least accurately localized. Though confined to the mouth, its more accurate limitations are not easily fixed. The point, sides and posterior sides of the dorsum of the tongue can appreciate tastes; and probably parts of the palate also have the power, but in a much less degree. Indeed, though "the palate" is often spoken of as if it were the seat of taste, it really enjoys an insignificant share of this function compared with the tongue.

The power of being stimulated by various tastes is not restricted to the terminals of any one nerve, but is shared by some of those of at least three trunks, which also transmit impulses arising from other forms of stimulation. The glossopharyngeal division of the 8th pair sends branches to the posterior part of the tongue, which are no doubt connected with the special taste organs. The lingual branches of the 5th-commonly called the gustatory nerve-have also terminals capable of being excited by taste, and probably some fibres of the chorda tympani are employed in this function.

In the furrows around the circumvallate papillæ, and also, but more sparsely, on the sides of the fungiform papillæ of the tongue, are found peculiar organs called "taste buds" or "taste goblets." They are imbedded in the stratified epithelium, with the cells of which their outer layers are intimately connected. They are flask-shaped bodies, composed of concentric series of modified epithelium cells arranged like the staves of a barrel, pinched together at the base and at the free surface, where they closely surround the projecting points of the central elements. These consist of nucleated bars, supposed to be the nerve terminals. The whole arrangement reminds one somewhat of the construction of the head of a ripe artichoke.

Nerves can be seen entering these bodies, and are in all probability directly connected with the modified epithelial cells of

FIG. 213.

1 and 2.

Drawing of upper surface of the tongue, showing the position of the papilla.
Circumvallate papillæ. 3. Fungiform papillæ. 4. Filiform papillæ. (Sappey.)

which they are made up.

The relation of the glosso-pharyngeal nerves to these taste buds has been shown by the fact that in the

rabbit (in which animal they are crowded together in a special organ so as to be easily found) they degenerate, and in a few months disappear, after one of these nerves has been cut.

The genuine taste sensations are very few. Much of what we commonly call taste depends almost exclusively upon the smell of the substance, and we habitually confuse the impressions derived from these two senses.* The different tastes have been divided into four, viz., sweet, sour, bitter and salty, under some

(Cadiat)

a, fibrous tissue of papilla; d and c, epithelial covering of papilla; b, taste buds. On the right, a, b, show the separate cells of a taste bud.

one or other of which headings all our tastes, properly so called, would naturally fall. Though this classification has no just claim to being a chemical one, it is interesting to know that each taste pretty well corresponds to a distinct group of substances chemically allied one to the other. Thus, acids are sour, alkaloids are

Many of the comestibles, the taste of which we most prize, have really no taste, but only a smell which we habitually confound with taste, having mingled the experience obtained from the two senses. Thus, if the draft of air be carefully excluded from the nose, wine, onion, etc., may easily be proved to have no taste. Hence the familiar rule of holding the nose adopted in taking medicine with a nasty "taste."

a

bitter, the soluble neutral salts of the alkalies are salty, and polyatomic alcohols, as glycerine, grape sugar, etc., are sweet.

These substances probably act on the nerve terminals as chemical stimuli, because they must be in solution to be appreciated. If solid particles be placed on the tongue they must be dissolved in the mouth fluid before they can excite the taste organs.

In order to explain the appreciation of the different tastes, we may imagine that there are different kinds of terminals, each of which is or is not influenced by various substances as they possess a special sweet, sour, bitter or salt energy. From these different terminals pass fibres bearing impulses to certain central cells, each of which is capable of exciting a sweet, sour, bitter or salty sensation, as the case may be.

SENSE OF SMELL.

The numerous delicate nerves which pass from the olfactory bulb to the mucous membrane of the upper and part of the middle meatus of the nose form the special nerves of smell. When certain subtle particles we call odors come in contact with the terminals of these nerves they excite impulses which, on arriving in the special centres of the brain, give rise to the impressions of smell.

Anatomically, the relations of the olfactory region are well defined. Its mucous membrane is not covered with motile cilia, as is that of the rest of the nasal cavity, and it is less vascular and peculiarly pigmented, looking yellow to the naked eye when compared with the neighboring membrane. The epithelial cells are elongated into peculiar cylinders, between which lie long thin rods, ending on the surface in free hair-like processes. The deeper extremities of these rod-shaped filaments expand to surround a nucleus, and are then continued into a network of filaments, into which prolongations of the epithelial cells also seem to pass, and in which the delicate fibrils of the olfactory nerve can be traced. The existence of direct communication between the nerves and the rod-shaped filaments and the epithelial cells is satisfactorily established in some animals.