series).

II. Aromatic odors (terpenes, camphors, and the spicy,
herbaceous, rosaceous, and almond series; the chemical types are
well determined: cineol, eugenol, anethol, geraniol,
benzaldehyde).

III. The balsamic odors (chiefly aldehydes, Rimmel's jasmin,
violet, and balsamic series, with the chemical types: terpineol,
ionone, vanillin).

IV. The ambrosiacal odors (ambergris and musk).

V. The alliaceous odors, with the cacodylic group (asafoetida,
ichthyol, etc.).

VI. Empyreumatic odors.

VII. Valerianaceous odors (Linnaeus's _Odores hircini_, the capryl
group, largely composed of sexual odors).

VIII. Narcotic odors (Linnaeus's _Odores tetri_).

IX. Stenches.

A valuable and interesting memoir, "Revue Generale sur les
Sensations Olfactives," by J. Passy, the chief French authority
on this subject, will be found in the second volume of _L'Annee
Psychologique_, 1895. In the fifth issue of the same year-book
(for 1898) Zwaardemaker presents a full summary of his work and
views, "Les Sensations Olfactives, leurs Combinaisons et leurs
Compensations." A convenient, but less authoritative, summary of
the facts of normal and pathological olfaction will be found in a
little volume of the "Actualites Medicales" series by Dr. Collet,
_L'Odorat et ses Troubles_, 1904. In a little book entitled
_Wegweiser zu einer Psychologie des Geruches_ (1894) Giessler has
sought to outline a psychology of smell, but his sketch can only
be regarded as tentative and provisional.

At the outset, nevertheless, it seems desirable that we should at least
have some conception of the special characteristics which mark the great
and varied mass of sensations reaching the brain through the channel of
the olfactory organ. The main special character of olfactory images seems
to be conditioned by the fact that they are intermediate in character
between those of touch or taste and those of sight or sound, that they
have much of the vagueness of the first and something of the richness and
variety of the second. AEsthetically, also, they occupy an intermediate
position between the higher and the lower senses.[26] They are, at the
same time, less practically useful than either the lower or the higher
senses. They furnish us with a great mass of what we may call
by-sensations, which are of little practical use, but inevitably become