PUNGENT AND ETHEREAL ODOURS.

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sensation interesting to study. It shows the effect of a sharp mechanical irritation of the nerves that does not amount to acute pain. A scratch, or a blow on the skin, an electric spark, a loud crash, a brilliant flame, a scorching heat, are all pungent effects, and seem to owe the pleasure they cause to the general excitement they diffuse over the system, and the lively expression that they give birth to. They rouse the system from ennui to enjoyment; they are a species of intoxication. They exalt for the time being the emotional condition of the human system. They come therefore to be one of the cravings associated with ennui, or depression of mind; they are likewise a stimulus for bringing out the exuberance of the auimal spirits among the young and vigorous, and those that lead a 'fast' life.

13. The ethereal is a distinct variety of the sensations of smell, and is probably a mixture of pungency with odour strictly so called. Alcohol and the ethers, including chloroform and the substance first employed as an anesthetic, will recal this effect. There can be no question but that alcohol and the vinous aromas have true odours; most probably, however, they have an influence upon other nerves than the olfactory; just as the fiery taste attributed to them is something beyond the gustatory feeling. At all events the odour is a distinct one, and is very different from the odours of vegetation and the common perfumes. It is not destitute of sweetness, but something besides sweet is wanting to express it.

The sulphurous and electrical odour is not radically different from the above class, so far as I am able to discriminate it. This odour has been traced to a particular substance discovered by Professor Schönbein and named by him ozone, from the Greek word signifying smell.

If we were to recognise a class of acrid odours, they would only be a mixture of pungency and bad smell; like many of the so-called empyreumatic odours resulting from the action of heat on vegetable bodies, as in the manufacture of coal gas.

14. The appetising smells might be treated as a class apart from the rest. The smell of flesh excites the carnivorous

appetite, and rouses the animal to pursuit. We may probably consider this influence as similar in its working to the first taste of savoury food; by the law of feeling-prompted movement, it sets on the activity for an increase of the gratification. A savoury smell may partly. give a commencing pleasure of digestion, and partly bring out into keenness and relief the sense of hunger; in either case it would fire the energy of pursuit towards the full fruition. The sexual excitement in some animals is induced by smell. Sympathy and antipathy are alike generated by odours. The influence of odours upon the voluptuous tender emotions has not escaped the notice of the poets. Cabanis observes that the odours of young animals are of a kind to attract, and he considers even to invigorate, the older.

15. It is remarked that bodies believed to have a strong taste, have often in reality only an odour; of which cinnamon is the common instance. Perhaps too in wine a large part of the effect in the mouth is in the smell. Hence the ambiguous term 'flavour' which is applied to solid and liquid substances, means most frequently the odour, or the mixed effect of taste and odour.

16. Smell, like taste, is an important instrument in the discrimination of material bodies, and therefore serves a high function in guiding our actions and in extending our knowledge of the world. Man does not exemplify the highest development of this organ. The order of ruminants, certain of the pachydermatous animals, and above all the carnivorous quadrupeds, excel the human subject in the expansion given to the membrane of the nose, and in a corresponding sensibility to odours. The scent of the dog is to us almost miraculous; it directs his pursuit, and tells him his whereabouts. It may act the part of sight in enabling him to retrace his steps or to find out his master.

SENSE OF TOUCH

1. Physiologists in describing the senses not unusually commence with Touch. This,' say Messrs. Todd and Bowman, 'is the simplest and most rudimentary of all the special senses, and may be considered as an exalted form of common sensation, from which it rises, by imperceptible gradations, to its state of highest development in some particular parts. It has its seat in the whole of the skin, and in certain mucous membranes, as that of the mouth, and is therefore the sense most generally diffused over the body. It is also that which exists most extensively in the animal kingdom; being, probably, never absent in any species. It is, besides, the earliest called into operation, and the least complicated in its impressions and mechanism.'

It may be well admitted that Touch is less complicated than Taste, where four different kinds of sensations may be said to meet, the tactile being one of them. It may be further said of touch, that the mode of action (mechanical contact or pressure), is the most simple and intelligible of any that we find giving rise to sensation. Nevertheless, there is one consideration that has prevailed with me in giving it a place subsequent to organic sensibility, taste, and smell. Touch is an intellectual sense of a far higher order than these. It is not merely a knowledge-giving sense, as they all are, but a source of ideas and conceptions of the kind that remain in the intellect and embrace the outer world. The notions of the size, shape, direction, distances, and situation of external bodies may be acquired by touch, but not by either taste or smell.

But this last assertion must be accompanied by an important explanation. Touch, considered as a source of ideas such as those, is really not a simple sense, but a compound of sense and motion; and it is to the muscular part of the sense, or to the movements of the touching organs that these conceptions owe their origin and their embodiment, as we have endeavoured to show in the previous chapter. The superiority

of touch to taste and smell, in this view, therefore, consists in its union with movement and muscular sensibility; and the same advantage pertains to sight. The contact of solid bodies with the surface of the body gives occasion to the exercise of movement, force, and resistance, and to the feelings and perceptions consequent on these: which cannot be said of smell, nor of taste properly so called.

A second feature marking the superiority of the sense of Touch, and qualifying it to furnish intellectual forms and imagery, is the distinctness or separateness of the sensations felt over the different parts of the skin. The sensations of the different parts of the surface of smell, would seem to fuse all into one stream of sensibility; it is not possible ever to refer a smell to any one portion of the membrane more than another. But the sensations of the skin are conveyed by distinct nervous filaments; each little area of skin has a separate nerve, and an independent communication with the nerve centres, whereby we can, after a little education, refer each sensation to the spot where the contact is made. The stimulus on one finger is not, at any part of the course of the nerve, confused with the stimulus on another finger; the back can always be distinguished from the breast, the right side. from the left, and so on. I shall afterwards endeavour to show that this localization of touches has to be learned by practice; but the very possibility of it rests upon the distinctness and independence of the nerve filaments. This is an extremely important fact, and makes the great difference between touch and what is called common sensation, or the sensibility diffused over all the internal organs and tissues. There is no such distinguishing sensibility in the stomach, or the lungs, or the liver; at all events, the distinctness of the nerves in those parts is very low in degree, just sufficient to enable us to refer a pain to the lungs, the liver, or the stomach, without indicating the particular region or subdivision. The skin is therefore marked by a great exaltation of the common sensibility of the body, not as regards intensity of feeling, but as regards distinctiveness of locality.

2. Having made these preliminary remarks, we commence

THE SKIN.

173 as usual, with the objects, or external agents concerned in the sense of Touch. These are principally the solid substances of the outer world. Gases do not act on the touch unless they are blown with great violence. The pressure of the atmosphere gives rise to no feeling, excepting from its temperature. Liquids also give very little feeling, if they are of the same warmth as the body. The sensations of a bath are confined to heat or cold, which are feelings that the skin has in common with other tissues. It is manifest that an even, equal pressure, such as fluids give, is not sufficient to impress the tactile nerves. The asperities and inequalities of solid surfaces, by pressing intensely on some points and not at all on others, are requisite for this purpose.

The hard unyielding nature of the mineral constituents of the earth's crust, metals, rocks, &c., are particularly well fitted to excite the touch. The woody fibre of the vegetable world has a compactness next in degree to the solid minerals. The soft and yielding class of solids impress the surface in a totally different manner: and these differ among themselves accord ing as they recover their form after pressure, or not; whence the distinction of elastic and non-elastic. When the substance is moved over the skin, the asperities come to be felt more acutely, and hence the further distinction into rough and smooth surfaces. In treating of the sensations themselves we shall attend to these qualities more minutely.

3. The sensitive organ or surface is the skin, or common integument of the body, the interior of the mouth, and the tongue. The parts of the skin are its two layers, its papillæ, the hairs and nails, its two species of glands,—the one yielding sweat, the other a fatty secretion,-with blood vessels and nerves. I shall quote a few extracts from the anatomical description of those parts. Of the two layers, the outermost is the cuticle, epidermis, or scarf skin. It forms a protective covering over every part of the true skin, and is itself quite insensible and non-vascular. The thickness of the cuticle varies in different parts of the surface, measuring in some not more than, and in others from to of an inch. It is thickest in the palms of the hands and soles of the feet, where