Heat operates by its volatilizing power, and by promoting decomposition. Light is a chemical influence. Moisture may dissolve solid matters and prepare the way for their being volatilized.

4. The gaseous property, called diffusion, determines peculiar manifestations in odours.

Some odours are light, and therefore diffuse rapidly, and rise high; as sulphuretted hydrogen. The aromatic and spice odours, by their intensity and diffusibility combined, are smelt at great distances; the Spice Islands of the Indian Archipelago are recognized far out at sea. The animal effluvia are mostly dense gases; they are slowly diffused and do not rise high in the air. In scenting, a pointer dog keeps his nose close to the ground. Unwholesome effluvia, very strong on the ground, are unperceived at the height of a few feet. In tropical swamps, safety is obtained by sleeping at a height above the ground.

5. The Organ of Smell is the nose, and the place of sensibility is the membrane that lines the interior and the complicated cavities branching out from it.

The nose is lined throughout with a mucous membrane; and the complicated bones adjoining it, give extension of surface to that membrane, whereby the sensibility is magnified. It is also an important fact, in the Anatomy of the organ, that the proper nerve of smell, called olfactory, is most copiously distributed in the interior recesses, and not at all near the entrance of the nostrils; to which part, twigs of the fifth pair are distributed, conferring upon it a tactile sensibility.

6. The mode of action of odours appears to be a process

of oxidation.

The facts in favour of that view were pointed out by Graham. Odorous substances in general are such as oxygen can readily act upon; for example, sulphurous hydrogen, and the perfumes. Again, gases that have no smell are not acted on by oxygen at common temperatures; the pure marsh gas, carburetted hydrogen, which has no smell, has been obtained from deep mines, where it has been in contact with oxygen for geological ages. It is farther determined that unless a stream of oxygen passes through the nose, there is no smell.

FRESH ODOURS.

FRAGRANT ODOURS.

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7. The Sensations of Smell are, first, those in sympathy with the Lungs; secondly, those of Smell proper; thirdly, those involving excitation of nerves of Touch.

Those in sympathy with the Lungs may be described by the contrasting terms-fresh and close odours.

Fresh odours are the feelings of exhilaration from the quickened action of the lungs. Certain odorous substances have that quickening efficacy, as eau de Cologne, lavender, peppermint, and many, but not all, perfumes; the spirit used in dissolving the essences being not unfrequently the source of the stimulus. These are the substances used for reviving the system depressed by the atmosphere of a crowd. Freshness may, or may not, be joined with fragrance; the odour of a tanyard is stimulating to the lungs; the smell of a cow is fresh and sweet. Musk is probably stimulating.

Close or suffocating odours arise from a depressed action of the lungs. The effluvia of crowds, and of vegetable and animal decay, the deficiency of oxygen, and the accumulation of carbonic acid, however caused, lower the powers of life, and are accompanied with a depressing sensation, which should properly be called a sensation of the lungs, but which we connect also with smell. The smell of a pastry-cook's kitchen is close and yet sweet.

Certain odours, as sulphuretted hydrogen, are nauseous or disgusting, which implies a sympathy with the stomach, although in what mode, or through what nerves, is not clear.

8. Connected with proper olfactory sensibility are fragrant odours and their opposites.

For sweet or fragrant odours we refer to the rose, the violet, the orange, the jasmine, &c. In them we have the proper pleasure of the organ of smell; the enjoyment derivable through the olfactory nerves. It is acute or massive, according to the concentration or diffusion of the material; compare an essence, as lavender, or rosemary, with a bed of mignonette or a field of clover. A certain degree of what is termed refinement attaches to the pleasures of pure smell; the stimulus is so gentle that it can be endured for a length of time without palling.

The opposite of sweetness is given in the expressive name stink; a milder substitute is malodour. The smell of assafotida is an example; some of our repulsive odours are in part disgusting, and do not represent pure olfactory pain. Va

lerian, rag-wort, and the seum of stagnant marsh (squeezed in the fingers) give forth malodours. Whenever the olfactory nerves are painfully irritated, this is the character of the pain. Amid many distinguishable varieties of bad smell, there is a common type of sensation.

9. Through excitation of the nerves of touch we derive the pungent odours.

Ammonia (as in smelling salts), nicotine, mustard, acetic acid, give rise to a sharp stinging sensation, for which the best name is pungency. It is most probably a mechanical irritation of the nerves of the fifth pair; habitual snuff-takers lose the pure olfactory sensibility. The general effect, named pungency, is a mode of nervous and mental excitement; within limits, it gives pleasure. A loud sound, a flash of light, a hurried pace, have a rousing effect, pleasurable, if the nerves are fresh and unoccupied, painful otherwise.

The ethereal odours, as alcohol and the aroma of wines, are partly fresh and sweet, and partly pungent.

There are odours that we may call acrid, combining pungency with ill smell, as the odour of coal-gas works.

The sensual appetites are, in many cases, fired by odours. The smell of flesh excites the carnivorous appetite; which may be due partly to association, and partly to that sympathy of smell with digestion, shown in the nauseous odours. Sexual excitement, in some animals, is induced by smell, as by many other sensations. There is here a general law, that one great pleasure fires the other pleasurable sensibilities. (See TENDER EMOTION.)

Some sapid bodies are also odorous. In the act of expiration accompanying mastication, especially the instant after swallowing, the odorous particles are carried into the cavities of the nose, and affect the sense of smell. This is flavour. Cinnamon has no taste, but only a flavour; that is, an odour brought out during mastication.

Viewing Smell in the Intellectual point of view, once for all, we find it considerably in advance of Organic Sensibility, if not of Taste also. The power of discrimination exercised by smell is very great; we derive much instruction and guidance by means of it. Yet higher in this respect is its development in many animals, as the ruminants, certain of the pachydermatous animals, and, above all, the carnivorous quadrupeds. The scent of the dog seems miraculous.

The power of recollection is usually in proportion to the

aptitude for discrimination; and in regard to smells, the power of recollecting is considerable. We can, by an effort, restore to mind the sweetness of a rose, the pungency of smelling salts, or the bouquet of an essence.

SENSE OF TOUCH.

1. As an intellectual, or knowledge-giving sense, Touch ranks decidedly above Taste and Smell.

The Objects of Touch are principally solid substances.

Gases do not affect the touch, unless blown with great violence. Liquids give little or no feeling, except heat or cold. A certain firmness of surface is necessary, such as constitutes solidity.

2. The sensitive Organ is the skin, or common integument of the body, together with the interior of the mouth, the tongue, and the nostrils.

The parts of the skin are its two layers-cuticle and true skin; the papillæ; the hairs and the nails; the two species of glands the one yielding sweat, the other an oily secretion; with blood vessels and nerves.

The cuticle is the protective covering of the skin, being itself insensible; it varies in thickness from the 1 to the of an inch; being thickest on the soles of the feet, and on the palms of the hands. The true skin lying underneath, and containing the papillæ, nerves, and blood-vessels, is the sentient structure. It is marked in various places by furrows, also affecting the cuticle, as may be seen in the skin of the hand. The papillæ are small conical projections, besetting the whole surface of the skin, but largest and closest on the palm of the hand and fingers, and on the sole of the foot. Their height on the hand is from too of an inch. Into them blood-vessels enter, and also nerves; and they are the medium of the tactile sensibility of the skin. The two sets of glands concern the skin as a great purifying organ. Very small muscular fibres have been discovered in the skin; they are easily affected by cold, and their contraction makes the shivering of the skin.

3. The action in Touch is simple pressure.

The contact of a firm body compresses the skin, and, through it, the nerve filaments embedded in the papillæ.

4. The Sensations of Touch may be arranged under the following heads :-the Emotional, and the Intellectual sensations of Touch proper; and the sensations combining Touch and Muscularity.

The first class includes soft Touches, pungent smarts, temperature, and some others.

Soft Touches. In these we suppose the gentle contact of some extended surface with the skin, as the under clothing, or the bed clothes. From such contact, results a pleasurable sensation, of little acuteness, but of considerable mass, when a large surface is affected. In most instances of pleasurable contact, there is warmth combined with touch, as in the embrace of two creatures of the warm blooded species, or in the contact of one part of the body with another. We become insensible to the habitual contact of our clothing, on the general principle of Relativity; but the transition to, or from, the naked state makes us aware of our sensibility to touch.

The mixed sensation of contact and warmth is strongly manifested in the clinging of the young to the mother, both in the human species and in the inferior tribes. The warm contact is maintained with great energy of will. It also determines many of the peculiar modes of expression in human beings; as the putting of the finger or the hand to the mouth and face, either as mere sensuous luxury, or as a solace in pain. In luxurious repose, a soft warm contact is desiderated for the hands.

Pungent and painful sensations of Touch. A sharp, intense, smarting contact with the skin, produces, up to a certain point, an agreeable pungency or excitement; beyond that, an acute pain of the physical class. This is precisely analogous to the effects of pungency spoken of under the foregoing Senses. Mere sensation, as such, is pleasurable within limits, when the nerves are fresh. Excitement is joyful to the unexpended nervous vigour; and this is gained by pungency.

The acute pains of the skin are illustrated in the discipline of the whip; a form of pain supposed to have both volitional efficiency at the moment, and intellectual persistency for the future.

Sensations of Temperature. We included the feelings of heat and cold among organic sensations. They are, in the vast majority of instances, connected with the skin, of whose sensibility they are a large and important item. The effect of changes of temperature on the nerves may still be mechanical,