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ought to have a considerable share of the saline in taste. Most mineral alkalies, and some earths and oxides of metals have characteristic tastes, rarely agreeable, and often not markedly disagreeable.

13. The sour or acid taste is much more uniform in its nature than either the saline or the alkaline; which we may fairly ascribe to the influence of the acid quality itself, irrespective of the constituent elements. This is a sharp, penetrating, pungent action, having, when very powerful, the pain more of a burn, than of a repulsive taste; in diluted forms it is an agreeable pungent stimulus to the mouth; hence the liking for vinegar (the sour of cookery as sugar is the sweet), and for acid fruits and vegetables. A galvanic current in the mouth causes sourness.

14. The astringent is a distinct form of the sensation of taste; as an example we may refer to the effect of alum in the mouth. It is evident, however, that in the acid action, and still more in this of astringency, we depart farther and farther from the proper feeling of taste. Astringent substances act on the skin and on the mucous membranes generally; and the influence lies in a kind of contraction or forcible shrinking of the part, to which we are sensitive whenever it occurs as a touch. The 'rough taste of tannin' may be put down under astringency.

15. The fiery taste of alcoholic liquors, mustard, pepper, camphors, and volatile oils, given in Gmelin's classification, seems to me to be happily designated. I am inclined to think that this too is more a tactile action than a gustative, although in some of the other substances entering with alcohol into wines, spirits, and malt liquors, there is a genuine stimulus of the taste. The acrid taste may be looked on as a form of the fiery, or astringent, combined with some ingredient of the bitter. On the other hand, the effect of peppermint resembles a cold contact on the skin. The pungency that marks all this class of sensations is a remarkable state of feeling, deserving to be once for all discussed at length. This discussion, however, I prefer to take

INTELLECTUAL CHARACTER OF TASTE.

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up under the sense of smell, the next in order in our arrangement.

16. With regard to the Intellectual aspect of Tastes in general, Longet observes that these sensations are deficient as regards the power of being remembered; and he gives as a proof the fact that, when we dream of being present at a repast, we see the viands but do not taste them. The fact is not beyond question, and besides, it is an extreme comparison; it contrasts the most intellectual of all the senses, the most abiding of all sensations, with those that are least So. It is so far true, that we do not recover sensations of taste so as to live habitually on the ideas of them, but they are slightly recoverable even as ideas, and for the purposes of identification and contrast, they may be recovered. to a very great extent. A wine tasted to-day can be pronounced the same or not the same as a wine tasted a week ago, while well marked tastes may be remembered for years in this way.

The intellectual character of the sense is also illustrated by its improvability. A wine-taster, a cook, or a chemist, can acquire a delicate sensibility to differences of taste, implying that its impressions can find an abiding place in the memory.

SENSE OF SMELL.

This sense is in close proximity to the organ of Taste, with which smell frequently co-operates; but we may consider it as placed at the entrance of the lungs to test the purity of the air we breathe.

1. The external objects of Smell, the material substances whose contact produces the sensations, are very numerous. They require to be in the gaseous state, in the same way that the objects of taste require to be liquified. Solids and liquids, therefore, have no smell except by being evaporated or volatilized.

The greater number of gases and vapours are odorous. Of inodorous gases, the principal are the elements of the

atmosphere, that is to say, nitrogen, oxygen, vapour of water or steam, and carbonic acid. In the long list of gaseous bodies recognized by the chemist, we find very generally some action on the nostrils,-carbonic oxide, sulphurous acid, chlorine, iodine, the nitrous gases, ammonia, sulphuretted and phosphoretted hydrogen, &c., the vapour of muriatic, nitric, and other acids. The singular substance ozone, produced occasionally in the atmosphere, is named from its smell, which is the smell of sulphur, and of the odour given forth by electricity. Some of the metals and solid minerals give out an odour, as, for example, the garlic smell of arsenic, and the odour of a piece of quartz when broken. The effluvia of the vegetable kingdom are countless; besides such widely spread products as alcohol and the ethers, a vast number of plants have characteristic odours, usually attaching to their flowers. The animal kingdom also furnishes a variety of odours; some general, as the 'scent of blood,' and others special, as musk, the flavour of the cow, the sheep, the pig. All volatile organic compounds,' says Gmelin, 'are odoriferous, and most of them are distinguished by very strong odours; e.g. volatile acids, volatile oils, camphors or stearoptenes, and alcoholic liquids; marsh gas (carburetted hydrogen), and olefiant gas, have but very little odour.'

The pleasant odours, chemically considered, are hydrocarbons; that is, they are composed chiefly of hydrogen and carbon. Such is alcohol and the ethers, eau de Cologne, attar of roses, and the perfumes. Many smells, however, elude investigation from the minuteness of the substance causing them. Thus the vinous flavour is due to a substance which the chemist has been able to separate, being termed the cnanthic ether; but the bouquet of individual wines has not been laid hold of.

With regard to carbonic acid, the assertion as to the absence of smell is true of the amount present in the atmosphere: but, collected in mass, this gas has a slightly pungent, somewhat acid odour. As with pungent odours generally, the effect is probably due to the irritation of the nerves of the fifth pair, and not to the proper olfactory sensibility.

THE CHEMISTRY OF ODOURS.

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The repulsive and disagreeable odours very frequently contain sulphur. Sulphuretted hydrogen is one of the most common of the disgusting class.

The worst smelling substances as yet discovered have arsenic for their base, as will be seen from the following extract. (GREGORY'S Chemistry, p. 382.)

'When acetate of potash is heated along with arsenious acid, a very remarkable liquid is obtained, which is the oxide of a new radical. This liquid, which is spontaneously inflammable, and has a most offensive alliaceous smell, has long been known in an impure state, under the names of liquor of Cadet, and alcarsine. Bunsen, by a long series of the most profound and persevering researches, established its true character as the oxide of the radical kakodyle.' This radical, when obtained, is a clear liquid, refracting light strongly. When cooled, it crystallizes in large square prisms, and acquires, when pure, the appearance of ice. Its smell is insupportably offensive, and its vapour is highly poisonous. The two latter characters belong to all the compounds of kakodyle, with hardly an exception.' Protoxide of kakodyle, the chief ingredient in the liquor of Cadet, is most offensive. to the smell, and very nauseous to the taste. 'Chloride of kakodyle is a volatile, horribly fetid liquid, the vapour of which attacks strongly the lining membrane of the nose, and provokes a flow of tears.'

The pungent odours have ammonia for their type. The volatile alkali, nicotine, the element of the snuffs, is an instance. In smelling salts, ammonia is the substance given forth.

Liebig has been able to lay hold of, and isolate, the substance that gives the odour of roast meat. Burning fat gives forth odours that exemplify the volatile oils specified by Gmelin.

2. The development or production of odours is favoured by a variety of circumstances. Heat, by its volatilizing power, and by promoting decomposition, is the most powerful agent. Light, also, which carries forward the development of the plant, is an odoriferous influence. Hence the abund

ance and variety of odours in warm and sunny climates, and in the summer season. The presence of moisture is often favourable; but the manner of acting of this agency is not always obvious. It may perhaps dissolve solid matters, and so put them in the way of being volatilized; this may be the cause of the evolution of perfumes after a shower. On the other hand, some flowers are most odorous when dried. Friction is a source of odours; by rubbing two pieces of flint or siliceous rock a smell is given forth; sulphur treated in the same way has a smell. Many of the metals have the same property. Doubtless some ingredient is volatilized by the rubbing action.

3. The diffusion of odours is an interesting point, and has been cleared up by the researches of Professor Graham. Some odours are light, and therefore diffuse rapidly and rise high; as, for example, sulphuretted hydrogen. Such is evidently the character of the aromatic and spice odours; they, by their intensity and diffusibility combined, are smelt at great distances. The Spice Islands of the Indian Archipelago are recognized far out at sea. It happens, however, that the sweet odours are remarkably persistent, while the sulphuretted compounds, which are among the most nauseous, are very rapidly destroyed in the atmosphere.

The animal effluvia (excepting sulphuretted hydrogen) are dense gases, and are diffused slowly. They do not rise high in the air. In scenting, a pointer keeps his nose close to the ground. The unwholesome effluvia of the decaying matter laid on the soil is avoided by getting to a moderate height; a person lying will smell what would not be smelt by one standing. The danger of sleeping on the ground in tropical swamps is a matter of fatal experience; swung in a tree fifty feet high, one may pass the night safely. Here diffusibility is one, although not the only circumstance; during the night, the ventilation or upward current from the ground is arrested, and the malaria, being little diffusible or buoyant, settles on the surface.

4. We have next to consider the organ of smell, that is

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