food, never discovered it, although several dogs had been attracted to it by the scent. His next experiment was to stick a young pig, and cover it over with leaves; vultures soon saw the blood, descended to it, and by this means soon discovered the pig, while it was still fresh. The general opinion of physiologists at present is, that birds of prey, have not so acute a sense of smell as has been generally supposed, and that they are guided chiefly by sight. 19. It is stated by whale-fishermen, that in Greenland, when a whale has been captured, although at the time scarcely a single bird may be visible, yet in a short time, immense numbers of gulls and other sea-birds hover about, and hasten to the spot from every point of the compass, Although these birds have the organ of smell, and consequently the sense itself, largely developed, yet such facts may be more satisfactorily explained, than by supposing that they are able to smell the flesh of a dead whale, before putrefaction has commenced, at a distance of many miles. A better explanation cannot be given than is contained in the first volume of "MacGillivray's History of British Birds."Speaking of ravens gathering together in immense numbers over a dead carcass, in explanation of the phenomenon he remarks, "A single raven might first perceive the carcass. Ravens have character in their flight as men have in their walk. A poet sauntering by a river, a conchologist or fishwoman looking for shells along the shore, a sportsman searching the fields, a footman going on a message, a lady running home from a shower, or a gentleman retreating from a mad bull, move each in a different manner, suiting the action to the occasion. Ravens do the same, as well as other birds; so those at the next station, perhaps a mile distant, judging by the flight of their neighbours that they had a prize in view, might naturally follow. In this manner the intelligence might be communicated over a large extent of country, and in a single day a great number might assemble. We know from observation that ravens can perceive an object at a great distance, but that they can smell food a quarter of a mile off we have no proof whatever; and as we can account for the phenomenon by their sight, it is unnecessary to have recourse to their other faculties." Every person who has seen the manner in which crows collect together about a dead animal in the country, will be satisfied that the above is a correct explanation of the pheno menon. 20. The olfactory organs of reptiles are but slightly developed. Frogs have two small holes, which serve as the organs of smell. The pituitary membrane of the turtle is of a very dark colour, and the nerve is of considerable size. In serpents, they are more elongated, and in lizards still more so. The animals of this class have no cavities corresponding to the sinuses; of course the sense of smell cannot be very acute. 21. The smell can be greatly improved by education. Humboldt states, that the Peruvian Indians can distinguish in the middle of the night the different races by their smell; whether they are European, negro, or American Indian. By habit, the perfumer acquires the faculty of distinguishing the nicest shades of odours. We see the influence of education, by the difference between a dog that has been trained to the chase, and one that has not. In the blind, the sense of smell is particularly acute. A boy in Edinburgh, who was born blind and deaf, could tell the entrance of a stranger into the room by the smell alone; and he told one person from another by smelling at him. 22. Dr. Good remarks, that "we occasionally meet among mankind with a sort of sensation altogether wonderful and inexplicable. There are some persons so peculiarly affected by the presence of a particular object, that is neither seen, tasted, smelt, heard, or touched, as not only to be conscious of its presence, but to be in agony till it is removed. The vicinity of a cat not unfrequently produces such an effect; and I have been a witness to the most decisive proofs of this in several instances." There can be no doubt, I think, that this peculiarity is referable to delicacy of smell. Dr. Dung. lison states, that a gentleman, blind from birth, had an extraordinary antipathy to cats. One day in company, he suddenly leaped up, got upon an elevated seat, and exclaimed, that there was a cat in the room, and begged them to remove it. It was in vain that the company assured him that he was mistaken. He persisted in his assertion and in his state of agitation; when, on opening the door of a small closet in the room, it was found that a cat had been accidentally shut up in it. Questions. Define the sense of smell. scribe the pituitary membrane ;—the nose. Where is it seated? De- ed in the sense of smell? What is the object of such an extended surface? How many bones assist in forming the cavities of the nostrils? Why are they supplied with muscles? Does the membrane that line the nostrils resemble the other mucous membrane? How is it moistened? Do the tears answer any purpose except washing the eye? What effect has snuff-taking on the sense of smell? What is the nerve of smell? What other nerves send twigs to the nose ;-their function? To what does Majendie compare the organ of smell? What is odour? How given off from bodies? Are odours easily described ? What facts show that their particles are very minute? What is the art of perfumery? Do odours differ as to the permanence of the impression they produce? What favours the diffusion of odours? Can odours be conveyed through water or other fluids? Have fishes any organ of smell? What facts prove this? What article renders bait attractive to fish? Were odours ever believed to be nutritious? What anecdotes in relation to this? Are the senses of smell and taste associated? What is the use of smell? Are any substances disagreeable to the smell and agreeable to the taste? Is smell more useful to animals than man? Is it infallible in them? What fact proves that it is not? What singular custom prevails among shepherds? What animals have the sense of smell the most acute? How is the smell of the hog employed in France? What is said of this sense in the greyhound? Was it ever employed to hunt savages? When and where ? Have birds any organ of smell? What does Humboldt say of the condor? What experiments did Audabon try, to prove that birds of prey are guided by sight instead of smell? What do whale fishermen say of birds in Greenland? How does Mr. MacGilivray explain the gathering together of so many birds over a dead carcase? Have reptiles any olfactory organs? Can this sense be improved by education? What causes the singular antipathy to cats, which we meet with in some persons? CHAPTER XVI. THE SENSE OF SIGHT. 1. THIS is the most refined and admirable of all our senses. By it especially we hold converse with the external world; and without it, we should not only be deprived of a large portion of the pleasures we now enjoy, but we should be unable to maintain our existence for any length of time. The wisdom, power, and benevolence of God are chiefly manifested to us through the sense of vision. 2. The eye is the organ of sight, and the most beautiful of all the organs of the senses. So admirable is its structure, so wonderful the provisions which adapt it to the pur poses for which it was designed by our Creator, that I shall give as full a description of it as my limits will allow ; and in order to an easy and clear comprehension of its structure and function, I shall first describe the coats of the eye, including the retina, or the expansion of the nerve of vision; then the humours of the eye, by the agency of which, the_ rays of light are concentrated so as to form an image upon the retina; and lastly, explain the laws of vision, the motions of the eye, and the means of protection against injury. 3. The Coats of the Eye.-The coats of the eye are generally reckoned as three in number, viz., the sclerotic, the choroid, and the retina besides these, there are the cornea, the iris, and the ciliary processes, which are viewed and described as appendages to these coats. 4. The sclerotic,* or outer coat, is the firm, opaque, fibrous substance which preserves the globular figure of the eye; and besides defending its internal delicate structure, serves for the attachment of those muscles which move the eye. It invests * From a Greek word, signifying hard. |