cow-dung smells of ambergris-(REDWOOD)-and that even nightsoil, under certain forms of treatment, assumes a powerful odour of this substance-(HOMBERG)-suggest lines of research, by following which a mode of manufacturing ambergris may hereafter be discovered. 4°. INSECT ODOURS.-Among animal odours of an agreeable kind, those given off by certain insects are deserving of mention. To entomologists, many strong-smelling insects are known, though some of these, of course, are far from being agreeable to our senses. Fig. 89. Cerambyx moschata. The Cerambyx moschata (fig 89), a coleopterous insect, derives its specific name from the musky odour it emits. Most of the ants of Europe give off, when crushed, a well-known penetrating odour of formic acid: those of Bahia in South America, which are very troublesome and destructive, give off when squeezed a strong smell of lemons (WETHERELL). tator of Linnæus has so strong an odour, that, when several of the insects are collected together, they may be scented at a distance of five or six hundred paces-(RAESEL). It is to the eating of these insects that Mr. Lloyd † is inclined to ascribe the remarkable odour emitted by the grayling (Thymallus vulgaris), which by different writers has been likened to that of thyme or of honey. The Gyrinus na I do not multiply examples of this kind, as nothing is yet known as to the chemical nature of the odoriferous substances which insects emit; nor have any of them as yet been employed for purposes of luxury or economy. Many reflections are suggested by the facts I have * Memoirs of the French Academy, 1711. + Scandinavian Adventures, i. 128. brought together in the present chapter. Want of space forbids me to indulge in more than one or two. First. One circumstance which presses very strongly upon our attention, is the extremely minute state of diffusion in which the odoriferous substances of animal origin still make themselves perceptible to our senses. A fragment of musk not only gives off a strong smell when it is first exposed to the air, but it continues to do so for an almost indefinite period of time. Yet the odour must be caused by particles of matter which are continuously escaping from the musk, so long as it continues exposed to the air. How inconceivably small in weight, how infinitely minute in size, the molecules must be of which this constantly-flowing stream of matter consists! And to vegetable perfumes the same observations almost equally apply. A morsel of camphor will for days fill a large room with its scent without suffering any material diminution in weight. A single leaf of melilot will for years preserve and manifest its sweet odour, and yet the quantity of coumarin it contains would probably be inappreciable by the most delicate balance. We know in this country how a stalk of mignonette, placed in an open window, will scent the air that enters, through the whole of a long summer's day. But in hot climates, especially during the morning and evening hours, this diffusiveness of perfumes is still more striking. "The odour of the balsamyielding Humeriads has been perceived at a distance of three miles from the shores of South America-a species of Tetracera sends its perfume as far from the island of Cuba-and the aroma of the Spice Islands is wafted out to sea."* The quantity of ethereal oil which gives its peculiar aroma to grape wine has been estimated at one-forty * MRS. SOMERVILLE'S Physical Geography, ii. 122. DELICACY OF THE ORGANS OF SMELL. 503 thousandth only of the bulk of the wine, and that which gives the aroma to roasted coffee, at one-fifty-thousandth of its weight; but the ozone which exists in the atmosphere is distinctly perceptible to the smell when mixed with five hundred thousand times its bulk of air. Second. The nicety of the bodily organs by which we perceive these extremely diluted perfumes is equally a subject for admiration. The sense of smell detects and determines the presence of these infinitesimally minute molecules. This is remarkable. But it does much more. It distinguishes between them, pronouncing the impression it derives from one class to the agreeable, and from another class the reverse. It then further pronounces upon the amount and kind of the pleasurable sensation produced by each, and this through a long series of varieties and degrees. How delicate the structure of the organs of smell must be! How suprising that they should continue uninjured and unimpaired, amid so much thoughtless usage, and for so long a series of years! Third. This history of the odours we enjoy illustrates in a remarkable manner, how, out of the most vile materials, chemistry, by its magical processes, can extract the sweetest and most desirable substances. How wonderful this power, how delightful to possess it, how useful its results! Artificial musk and ambergris! Manufactories of oil of bitter almonds! Essences of spiræa and winter-green prepared in chemical laboratories! Humble wines successfully flavoured to compete with the produce of the most costly vintages! Ethereal fragrances without number, and unknown by name, added to the list of enjoyable odours! Pleasing scents, in cheap abundance, of which the wealthiest in ancient times. could form no conception, and which they had no means of obtaining! This history presents, in truth, another striking illustra tion of the way in which modern chemical research leads to the establishment of new arts and manufactures-to the ad. dition of new and unknown luxuries to those already within our reach-to the cheapening of luxurious comforts to all,— and thus to the refining, and softening, and polishing of the whole community. It displays, also, to the reader the existence of a new field of practical and economic research which is almost boundless, shows how valuable chemistry is in almost every walk of life, and how the studies of the laboratory may be made a source even of money profit in the most unexpected departments of economic pursuit. THE CHAPTER XXVI. SMELLS WE DISLIKE. NATURAL SMELLS. Difference of opinion as to smells.-Disagreeable mineral smells.-Sulphuretted hydrogen; its properties, and production in nature.-Sulphurous acid given off from volcanoes; its suffocating reputation.-Muriatic acid gas.-Unpleasant vegetable smells.-Garlic and the onion.-Oil of garlic.-Sulphuret of allyle.-Sulphur an ingredient of many fetid smells.-Assafoetida, a concrete juice.-Oil of assafoetida. -Extensive use of vegetable substances containing allyle; they satisfy some natural craving; extensive distribution of them in nature.-Horse-radish and mus tard also contain allyle.-The stinking goosefoot.-The peculiar strong-smelling compound contained in this plant exists also in putrid fish; economical use of it in the cuisine.-Carrion plants.-The saussurea and the stapelias.-Smells often disagreeable only because of the things or memories associated with them.-Disagreeable animal odours; the goat, the badger, and the skunk.-Effects of minute doses of sulphur and tellurium.-Stenches as weapons of defence.-Insect smells. -The putrefaction of animal bodies; conditions which promote it; substances given off; their unwholesome character.-Burying-vaults and graveyards.-The droppings of animals; peculiar substances and smells given off by these. THE smells we dislike are probably quite as numerous as the odours we enjoy. Between the two, however, there is a wide debatable ground, in regard to which the utmost diversity of opinion prevails. What is fragrance to one person is sometimes abomination to another. Plutarch tells us that a Spartan lady paid a visit to Berenice the wife of Dejotarus; but that one of them smelled so much of sweet oint |