The aromatic substances here enumerated are those which have actually found general employment in perfumery; but the list is not complete, since every aromatic plant can be used for the extraction of its odor. Of course, this is connected with some difficulties, but even in the present state of our knowledge they can all be overcome. When a new odor has been prepared, the art of the perfumer consists in ascertaining by many experiments those substances which harmonize with it; for with few exceptions the finest grades of perfumes are not single odors but combinations of several which are in accord. Even among our domestic plants there are numerous finds to be made by the perfumer, and in this respect we refer particularly to some very fragrant kinds of orchids in our woods and to the delightful odor of the lily of the valley. As to the latter, a perfume is met with in commerce under this name, but its odor bears no resemblance to that of the flower. A few facts appear to us of especial importance. In practical perfumery many of the plants which are easily obtainable in large quantities, such as the flowers of clover and trefoil, the primrose, the rock-rose (Daphne Cneorum), dame’s-violet (Hesperis matronalis), and others above named, have never been employed. As an actual curiosity we may state that there is thus far no perfume containing the delightful odor present in the flowers of the linden-tree, of the Robinia (erroneously called Acacia), of the lilac, etc., at least not made from the plants here named. CHAPTER V. THE ANIMAL SUBSTANCES USED IN PERFUMERY. While the vegetable kingdom offers us an abundance of aromatic odors the end of which it is impossible to foresee, the animal kingdom contains absolutely no substance which may be called sweet-scented in the strict sense of the term. If we find nevertheless a few animal substances generally used in perfumery, they should be considered rather as excellent means for fixing subtle vegetable odors than as fragrant bodies in the true sense. By themselves, indeed, they have an odor, but to most persons it is not agreeable even if properly diluted. Thus far only five substances of animal origin are employed in perfumery, namely: ambergris, castor, hyraceum, musk, and civet. AMBERGRIS. _Latin_—Ambra grisea; _French_—Ambregris; _German_—Ambra. This is a substance whose origin is still doubtful; many facts indicate that it is a secretion—whether normal or morbid may be left undecided—of the largest living mammal, namely, of the pot-whale (Physeter macrocephalus). Ambergris is found in the intestines of this animal or, more frequently, floating about in the sea; the shores of the continents bordering the Indian Ocean furnish the largest amount of this peculiar substance.