In a book devoted to the production of perfumes it would certainly be in place to say something about the physiological relations of the olfactory sensations; but unfortunately this interesting part of physiology is still enveloped in great obscurity. All we know positively on this subject is that many particles of the odorous bodies evaporate and must come in contact with the olfactory nerves in order to produce the sensation of odor. There is no lack of experiments seeking to draw a parallel between sensations of smell and those of hearing, and, as is well known, we speak of a harmony and dissonance of odors as we do of tones. Piesse, the renowned perfumer, has even made an attempt to arrange the different odors in a “harmonic scale” having the compass of the piano, and to deduce therefrom a law for the mixture of the several aromatic substances. This attempt, although very ingenious, still lacks a scientific foundation. Piesse endeavors to combine the several scents like tones to produce chords in different scales; the chords of odors are to agree with those of tones. Thus far, however, no proof has been furnished that the olfactory nerve and the acoustic nerve have the same organization, and under this supposition alone could Piesse’s system be accepted as correct. THE DIVISION OF AROMATIC SUBSTANCES ACCORDING TO THEIR ORIGIN. The majority of the substances used in perfumery are derived from the vegetable kingdom, but some come from the animal kingdom, and for others which do not occur complete in nature we are indebted to chemistry. As is well known, most blossoms possess a decided odor, which is extremely fragrant in some; yet it is not the blossoms alone, but in different genera various parts are distinguished by agreeable odors. In some plants the fragrant substances are contained in every part, as in different pines and the mints; in others, only in the fruits (nutmeg, vanilla), while the other parts are odorless; in certain plants only the rinds of the fruits contain an aromatic substance (oranges, lemons). In the Florentine Iris the entire plant is odorless—only its root stock possesses an agreeable, violet-like scent; while, for instance, in the camphor-tree an aromatic substance exists in the wood, in the cinnamon laurel in the bark, in the clove-tree mainly in the closed buds. But taking the aromatic plants all together, we find that it is particularly their flowers which contain the finest odors, and that the majority of perfumes are prepared from their blossoms. From the animal kingdom we take for the purposes of perfumery only a very small number of substances, among which, moreover, some peculiar relation exists; while, for instance, all men would call the odor of violets, roses, vanilla, etc., agreeable, the odor of some animal substances is decidedly obnoxious to many persons, though others like it—an observation which can be verified often with reference to musk.