Parker notes it as worthy of remark that man has created, both accidentally and intentionally, many new odours—smells, that is to say, which have no fellow in the world of Nature—and he emphasises the fact that the nose is nevertheless capable of appreciating such novel sensations. In this connection we may mention that the art of modern perfumery can imitate closely many of the natural perfumes, and more particularly the natural flavours, by mixing together essences, or components, which in no way resemble the final product. Thus the flavour of peaches can be compounded artificially of aldehyde, acetate, formate, butyrate, valerianate, œnanthylate, and sebate of ethyl, and salicylate of methyl, with glycerine, glycerine being added to the fruit essences, as it is to wines, in order to restrain the evaporation of the volatile bodies. (The fruit essences are used only in the making of flavours. They cannot be employed as perfumes, as they are too irritating to the nose.) The union of components to form a product different from any one of them is found also in vision. When the colours of the spectrum, for example, are commingled, the resultant white light is devoid of any colour. Thus the potential responsiveness of the olfactory organ seems to be practically inexhaustible. So far, at all events, it has not yet reached the limits of its capacity. The number and variety of recognised smells being so great, then, one can readily understand how difficult it is to construct a classification of odours. Many attempts have, in fact, been made, but, depending as they do more or less upon subjective sensation, no two classifiers give us the same classification. Indeed, a division of all smells into “nice,” “neutral,” and “nasty” would be about as good as many much more ambitious efforts. Zwaardemaker’s is the classification most usually followed at present, and as it is to him we owe most of our knowledge of scientific olfaction, we shall detail it here: (1) Ethereal or fruity odours; (2) aromatic, including as sub-classes camphrous, herbaceous, anisic and thymic, citronous, and the bitter almond group; (3) balsamic, with sub-groups floral, liliaceous, and vanillar; (4) ambrosial or muscous; (5) garlicky (including garlic), oniony, fishy, and the bromine type of odour; (6) empyreumatic (guaiacol); (7) caprylic (valerianic acid); (8) disgusting; and (9) nauseating. The subjective character of these classes is obvious, especially in the last two groups, but, apart from that objection, most people will be inclined to protest when they learn that chloroform and iodoform are put into the first, the ethereal or fruity, group, while it is suggested, though to be sure with a query, that coffee, bread, and burnt sugar may belong to the “repulsive” (pyridine) group!