In man, the sense of smell is not ordinarily so acute as it is in many of the lower animals ; yet it is very possible that it may be capable of taking cognisance of a greater variety of odours. In the selection or his food, it is to him by no means the infallible guide that it seems to be in many other races ; for it not only gives no warning, in many instances, of what is noxious, but renders certain poisonous substances (as, for instance, those charged with prussic acid or the essential oil of al monds) positively attractive. So, again, in regard to the respiratory organs, whilst it gives warning of the presence of certain gases and emanations which are injurious, it takes no cognisance of many others which are not less hurtful. In the ordinary conditions of civilised life, man is not dependent upon his sense of smell for many of the ends which it answers in other animals ; hence this sense is altogether subordinate to others, and the want of it is not usually attended with any great inconvenience. But the case is ffir different among savage tribes, to whom it is as impor tant as it is to other animals in a state of nature, and in whom it seems to acquire, by the constant habit of attention to its indica tions, a similar acuteness. Thus, it is stated by Humboldt that the Peruvian Indian, in the middle of the night, is informed of the proximity of another individual by his smell, and can distinguish by his smell whether the stranger be an European, an American Indian, or a Negro. It has even been asserted that some other savage tribes of mankind are enabled to follow a track by the scent of the footsteps, like the bloodhound. The sense of' smell, moreover, usually acquires great acute ness, when, from deficiency of the other senses, its indications become the chief or only means of recognising bodies not in immediate con tact with the individual. Thus, in the well known case of James Mitchell, who was deaf, blind, and dumb from his birth, it was the principal means by which he distinguished persons, and enabled him at once to perceive the entrance of a stranger. Mr. Wardrop gives the following curious account of the mode in which he exercised this sense, and of the information which he derived from it :— " There were some people whom he never permitted to approach him, whilst others at once excited his interest and attention. The opinions which he formed of individuals, and the means he employed to study their charac ter, were extremely interesting. In doing this, he appeared to be chiefly influenced by the irnpressions communicated to him by his sense of smell. When a stranger approached him, he eagerly began to touch some part of his body, comnionly taking hold of the arm, which he held near his nose, and after two or three strong inspirations through the nostrils, lie appeared to form a decided opinion regard ing him. If this was favourable, he showed disposition to become more intimate, ex amined more minutely his dress, and ex pressed by his countenance more or less satis faction ; but if it happened to be unfavourable, he suddenly went off to a distance with ex pressions of carelessness or disgust. When he was first brought to my house to have his eyes examined, he both touched and smelled several parts of my body ; and the following day, whenever he found me near him, he grasped my arm, then smelled it, and imme diately recognised me, which he signified to his father by touching his eyelids with the fingers of both hands, and imitating the ex amination of his eyes which I had formerly made." We learn from the same account, that in selecting his food, he was always guided by his sense of smell, for he never took anything into his mouth without previously smelling it carefully. He always recognised his own clothes by their smell, and refused to wear those which belonged to others.
Sometimes the peculiar acuteness of this sense is restricted to a particular odour or class of odours, these usually proceeding from objects for which there is either a special fondness or a particular aversion. Thus, a
gentleman blind from birth, who had an unac countable antipathy to cats, so that he could never endure the presence of one in his apart ment, one day, when in company, suddenly leaped up and exclaimed that a cat was in the room, begging his friends to remove it. It was in vain that, after careful inspection, they as sured him that he was under an illusion. He persisted in his assertion, and his agitation con tinued ; and on the door of a small closet being opened, it was found that a cat had been accidentally shut up in it.
With such unequivocal proofs of the acute ness of the sense of smell which may exist in the human subject, the statements made re specting the extraordinary exaltation of the faculty in various forms of somnambulism be come less incredible ; and the author is fully satisfied, from his own observations upon in dividuals hypnotised by Mr. Braid (see SLEEP), that this exaltation may certainly take place in regard to the sense of smell. In one in stance, a glove being placed in the hand of the hypnotised subject, he found out the owner of it without difficulty, from amongst more than sixty persons, scenting at each of thein, one after another, until he came to the right individual. And in another case, the owner of a ring was in like manner unhesi tatingly found out from amongst a company of twelve.
The information conveyed by the sense of smell is restricted to the quality and intensity of the odour, and to some general notion of its direction. This last, indeed, is rather de rived front a comparison of its relative inten sity when the face is turned towards different sides, than from any more direct information as to locality furnished by the organ itself. The absence of any consciousness of the part of the olfactory surface specially affected by the impression,—so that, unless the experiment be made, we know not that we are constantly exerting the sense on both sides, the double sensation being perceived as a single one,— is attributed by Messrs. Todd and Bowman*, with much probability, to the peculiarplexiforin arrangement of the filmes of the olfactive nerve, and to the want of the isolation usually effected between the fibres by the white sub stance of Schwann.
Various classifications of odours, founded upon the impressions which they make upon the sense of smell, have been proposed ; but they are all liable to the objection, that there seems to be more of individual diversity in regard to the character of olfactory impres sions, than with respect to those of any other kind. Many odours, by some persons thought intolerable, are very agreeable to others ; thus, assafeetida is known amongst some by the name of " devil's dung," whilst by others it is spoken of as " food for the gods." It was commonly employed by the ancients as a con diment; but the individuals who thus relish it in our own country certainly' constitute the exceptions to the mass. So, again, the fumet of game, so highly valued by the epicure, is disagreeable to most persons who have not been trained to appreciate it. On the other hand, the aroma of certain flowers, which is peculiarly agreeable to most persons, is by no means so, or perhaps the reverse, to others. Thus, Midler remarks that the smell of mig nonette is to him only herb-like; whilst the flower of Iris Persica has been pronounced to be of pleasant odour by forty-one out of fifty four persons, by four to have little scent, by eight to be without all odour, and by one to be ill-scented.f It more frequently happens, in regard to odours and savours, than with respect to other sensory impressions, that habit renders that agreeable, and even strongly relished, which was at first highly repugnant.
(W. B. Carpenter.)