* Dunglison's Physiology.

14. A singular custom, which prevails among shepherds in some countries, shows that the sheep is more under the guidance of smell than sight or any of the other senses. " When a lamb has died," says Aitkin, " the shepherd wishes to put to the ewe another lamb that may have lost its dam; if she refuses to foster the stranger, he is sure to succeed by stripping off the skin of her own offspring, and tying it on the back of the stranger, that she may smell the skin ; she then entertains and treats it as her own. In this case she neglects the sense of sight, for nothing can be more uncouth than the object of her affections ; neither does she attend to the evidence afforded by hearing ; however unlike the bleating of the foster lamb may be to that to which she was first accustomed, her smelling is satisfied, and she is content." The same practice succeeds with the cow.

15. In the elephant, the tapir, and the hog, as well as in oxen, sheep, deer, and antelopes, we find the cavities of the nose very capacious, and the surface of the pituitary membrane vastly extended ; and accordingly the sense of smell is proportionally acute. In France it is customary to employ the hog to hunt for truffles, a species of edible mushroom which grows at some distance below the surface of the ground. By the sense of smell alone, he is accurately guided to the spot where one is growing, and begins to turn up the earth with his snout, in order to get at it. The vegetable hunter, however, anticipates him, and driving away the animal, digs down, and appropriates it to himself. In this way he secures, in a short time, sufficient for a family dinner.

16. The delicacy of this sense in the greyhound is most astonishing. He not only tracks the hare, the fox, or the wolf with unerring certainty, long after their footsteps have been imprinted, but even in a large city, he will trace the progress of his master through thoroughfares and thickly crowded streets, distinguishing his footsteps from those of a thousand passers by, and amidst the odorous particles emanating from a thousand sources. When Hispaniola was first discovered by the Spaniards, they employed the greyhound in hunting the poor natives, who, unlike the more fortunate Seminoles of Florida, could find no ever glade, no fastness, no retreat, which could save them from the unerring scent of these animals.

17. The organ of smell is universally found in birds, though varying in size. Rapacious birds and waders, or those that live on fish, have it more largely developed than any others. Humboldt relates that in South America, when the inhabitants wish to take the condor, they kill a horse or cow, and in a short time, the odour of the dead animal attracts those birds in great numbers, and even in places where they were scarcely known to exist. Some of the Roman historians tell us that vultures went from Asia to the field of battle at Pharsalia, a distance of several hundred miles, attracted thither by the smell of the dead. Pliny, the natural historian, affirms that the vulture and the raven have the sense of smell so delicate, that they can foretell the death of a man three days beforehand.

18. Mr. Audubon, however, relates two experiments to show that vultures are indebted to sight rather than smell, in the discovery of their prey. He stuffed a deer's skin with hay, allowed it to become as dry as leather, and placed it in a field ; in a few minutes a vulture made for it, attacked it, tore open the stitches, and pulled out the hay. He then put a dead hog into a ditch, and covered it over with care ; it soon putrefied and became intolerably offensive, but the vul tures, which were sailing about in all directions in search of 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 earcass. Ravens have character in their flight as men have in their walk. A poet sauntering by a river, a conchologist or fish woman 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 unne cessary 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 phenomenon.

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. Where is it seated ? Describe the pituitary membrane ;-the nose. What Savities are concerned 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 nestrils resemble the other mueous 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 1 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 rep. tiles any olfactory organs ? Can this sense be improved by education ? What causes the singular antipathy to cats, which we meet with in some persons ?