PLEASURES AND PAINS OF DIGESTION.

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to its intensity as pleasure. The acute stage of relish is succeeded by the more voluminous pleasure of Repletion, whose seat is in the surface of the stomach, the part engaged in the digestion of the food; a massive exhilaration, closely allied to agreeable warmth, and to the elation of stimulants.

The physical concomitants of Hunger are a collapsed condition of the stomach, and a deficiency of nutritive material in the system. Of the feeling itself, the first stages are mere depression or uneasiness; next come on gnawing pains referred to the region of the stomach, and in part muscular; these are followed by sensations of a more massive character, derived from the system at large, and indicating the stage of inanition or starvation.

Nausea and Disgust express a mode of powerful feeling characteristic of digestion, as suffocation is of the lungs. The feeling is associated with the act of vomiting; the wretchedness of it in extreme cases, as sea-sickness, is insufferable. The sensation is unique. The healthy routine of comfortable digestion is exchanged for a depression great in mass, and aggravated by acute nervous suffering. The memory of this state is an active recoil from whatever causes it; hence disgust is a term for the most intense repugnance and loathing.

The pains of Deranged Digestion are numerous. Some are extremely acute, as spasm in any part of the intestine. Many forms of indigestion are known simply as inducing a depressed tone, or interfering with the exhilaration of healthy meals. Sluggishness of the bowels is attended with massive depression; the re-action brings a corresponding buoyancy.

Under the present head may be classed the feelings connected with the sexual organs, the mammary glands in woman, and the lachrymal gland and sac. These are the result of organic processes in the first instance; but they enter into complicated alliances, to be afterwards noticed, with our special emotions.

There still remain the important organic functions of the Skin, which are attended with pleasurable and painful sensibilities. They will be noticed under the sense of Touch.

In the Muscular Feelings, together with the Organic Sensations now enumerated, arises that large body of our sensibility denominated physical Comfort and Discomfort.

SENSE OF TASTE.

1. The sense of Taste, attached to the entrance of the alimentary canal, is a source of pleasure and pain, and a means of discrimination, in taking food.

The Objects of Taste are chiefly the materials of food.

Of mineral bodies, water is without taste. But most liquid substances, and most solids that can be liquified or dissolved, have taste; vinegar, common salt, alum, are familiar instances.

Nearly all vegetable and animal products, in like manner, are characterized by taste. A few substances are insipid, as white of egg, starch, gum; but the greater part exhibit well marked tastes; sweet, as sugar; bitter, as quinine, morphine, strychnine, gentian, quassia, soot, &c.; sour, as acids generally; pungent, as mustard, pepper, peppermint; fiery, as alcohol.

2. The Organ of Taste is the tongue, and the seat of sensibility is its upper surface.

The upper surface of the tongue is seen to be covered with little projections called papillæ. They are of three kinds, distinguished by size and form. The smallest and most numerous are conical or tapering, and cover the greatest part of the tongue, disappearing towards the base. The middle-sized are little rounded eminences scattered over the middle and fore part of the tongue, being most numerous towards the point. The large-sized are eight to fifteen in number, situated on the back of the tongue, and arranged in two rows at an angle like the letter V. The papillæ contain capillary blood vessels. and filaments of nerve, and are the seat of the sensibility of the tongue.

Two different nerves supply the tongue; branches of the nerve called glosso-pharyngeal (tongue and throat nerve) are distributed to the back part; twigs of the fifth pair (nerve of touch of the face) go to the fore-part. The effect, as will be seen, is a two-fold sensibility; taste proper attaches to the first named nerve, the glosso-pharyngeal; bitter is tasted chiefly at the back of the tongue. Taken as a whole, the sensibility of the tongue is distributed over the whole upper side, but less in the middle part and most in the base, sides, and tip.

The relish of food increases from the tip to the back,

TASTE IN SYMPATHY WITH DIGESTION.

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which is an inducement to keep the morsel moving backwards till it is finally swallowed.

The indispensable condition of taste is solubility. Also the tongue must not be in a dry or parched condition. The sensibility is increased by a moderate pressure; and is deadened by cold.

No explanation has yet been given of the mode of action on the nerves during taste. It is probably of a chemical nature, resulting from the combination of the dissolved food with a secretion from the blood-vessels of the papillæ.

3. The Sensations of Taste fall under a three-fold division: (1) those in direct sympathy with the Stomach, as Relish; (2) Taste proper, and (3) Touch.

As to the first, there is an obvious continuity of structure in the Tongue and Alimentary canal, a common character of surface as regards mucous membrane, glands, and papillæ. Moreover, apart from taste proper, the feeling in the tongue indicates at once whether a substance will agree or disagree with the stomach; the tongue is in fact the stomach begun. And farther, what we call relish is distinct from taste; butter and cooked flesh are relishes; salt and quinine are tastes; the one varies with the condition of the stomach, being in some states converted into nausea, as in sea-sickness; the other remains under all variations of the digestive power.

4. The Tastes in sympathy with the Stomach are Relishes and Disgusts.

Relishes, as already explained, are the agreeable feelings arising from the kinds of food called savoury, as animal food, and the richer kinds of vegetables. Sugar is both a relish and a taste. As a feeling of pleasure, a relish is more acute and less massive than the digestive sensations, but less acute and more massive than mere sweetness of taste. The speciality of the feeling is the alliance with digestion. What possesses relish may be hard to digest, but will not be nauseous in the stomach. The strength of this feeling is farther measured by its volitional urgency, or spur to the act of eating. The intellectual persistence is not high.

Relishes imply their opposite, disgusts, in which the stomachic sympathy is equally apparent, and which may be similarly characterized with reference to the corresponding digestive sensation.

5. Taste proper comprehends Sweet and Bitter tastes.

Sweetness is typified in the taste of sugar, to whose presence is owing the sweetness of fruits and articles of food generally. This sensation may be called the proper pleasure of taste, or the enjoyment derivable through a favourable stimulus of the gustatory nerves. In Degree it is acute; in Speciality we recognize it as possessing a character, indescribable in language, but not confounded with the pleasure of any other sense. Its volitional character accords with its nature as pleasure. It is more intellectual than Organic sensations generally, or than Relish; we can discriminate its degrees better, and remember it better. Taste may be the lowest of the five senses, as regards intellectual properties, but it is above the highest of the organic group.

Bitter tastes are exemplified in quinine, gentian, bitter aloes, and soot. This, and not sourness, is the opposite of sweet; it is the proper pain of taste, the state arising by irritating, or unfavourably stimulating, the gustatory nerve. The characteristics are the same, with obverse allowance, as for sweetness.

6. In the third class of tastes, there is present an element arising through the nerves of Touch. Pungency is their prevailing character. They include the saline, alkaline, sour or acid, astringent, fiery, acrid.

The saline taste is typified in common salt.

It is neither

sweet nor bitter, but simply pungent or biting; and, in all probability, the sensation is felt through the nerves of the fifth pair. In some salts, the pungency is combined with taste proper; Epsom salts would be termed partly saline, and still more decidedly bitter.

The alkaline taste, as in soda, potash, or ammonia, is a more energetic pungency, or more violent irritation of the nerves; the pungency amounting to acute pain, as the action becomes destructive of the tissue.

The sour or acid taste is the most familiar form of pungency, as in vinegar. The pain of an acid resembles a scald rather than a bitter taste. The pleasure derivable from it is such as belongs to pungency, and must observe the same limits.

The astringent is a mild form of pungency; it is exemplified by alum. The action in this case has manifestly departed from pure taste, and become a mere mechanical irritation of the nerves of touch. Astringent substances cause a kind of shrink

ing or contraction of the surface; an effect imitated by the drying up of a solution of salt on the skin. What is called a 'rough' taste, as tannin, is a form of astringency.

The fiery taste of mustard, alcohol, camphor, and volatile oils, is of the same generic character, although more or less mixed with taste proper. The acrid combines the fiery with the bitter.

SENSE OF SMELL.

1. The Sense of Smell, placed at the entrance of the lungs, is a source of pleasure and pain, and a means of discrimination as regards the air taken into the lungs.

This sense is also in close proximity to the organ of Taste, with which smell frequently co-operates.

2. The Objects of smell are gaseous or volatile bodies, the greater number of such being odorous.

The chief inodorous gases are the elements of the atmosphere, that is, nitrogen, oxygen, vapour of water, and carbonic acid (in the small amount contained in the air). Carbonic oxide, sulphurous acid, chlorine, iodine, the nitrous gases, ammonia, sulphuretted and phosphuretted hydrogen, and the vapour of acids generally, are odorous. The newly discovered ozone, is named from the odour it gives. Some minerals give forth odorous effluvia, as the garlic odour of arsenic, and the odour of a piece of quartz when broken. The vegetable kingdom is rich in odours; many plants are distinguished by this single property. Animal odours are also numerous.

The pleasant odours, chemically considered, are hydrocarbons; they are composed chiefly of hydrogen and carbon. Such are alcohol and the ethers, eau de Cologne, attar of roses, and the perfumes generally. Of the repulsive and disagreeable odours, one class contain sulphur, as sulphuretted hydrogen. The worst-smelling substances yet discovered have arsenic for their base. Such are the kakodyle series of compounds discovered by Bunsen, from the study of a substance long known as liquor of Cadet.' The pungent odours are typified by ammonia; nicotine, the element of the snuffs, is an analogous compound.

3. The development of odours is favoured by Heat, and by Light. The action of Moisture is not uniform.