by savoury smells upon the appetite. It is not probable, that absorp tion can occur to a sufficient extent to account for the apparent satiation. The fact can only be explained by the impression upon the nervous system, which influences the appetite materially, as we see in the effect of various mental emotions. The first impact of a nauseous odour, or even the view of a disgusting object, frequently converts the keenest appetite into loathing. Yet, anciently, it was believed, that life might be sustained for a time, by simply smelling nutritious substances. Democritus is said to have lived three days on the vapour of hot bread; and Bacon refers to a man who supported an abstinence of several days by inhaling the odour of a mixture of aromatic and alliaceous herbs. Two hundred years ago these notions were entertained to a great extent; and they suggested the viaticum for travellers proceeding to the moon, according to the plan proposed by Dr. John Wilkins, Bishop of Chester. "If we must needs feed upon something," he remarks, "why may not smells nourish us? Plutarch and Pliny, and divers other ancients, tell us of a nation in India that lived only upon pleasing odours; and it is the common opinion of physicians that these do strangely both strengthen and repair the spirits." Fuller, a learned cotemporary of the bishop affords an amusing instance of litigation, originally given by Rabelais,3-whom he does not cite, however, -arising from this supposed nourishing character of odours. A poor man being very hungry, stayed so long in a cook's shop who was dishing up the meat, that his stomach was satisfied with the smell thereof. The choleric cook demanded of him pay for his breakfast; the poor man denied having had any; and the controversy was referred to the decision of the next man that should pass by, who chanced to be the most notorious idiot in the whole city: he, on the relation of the matter, determined that the poor man's money should be put betwixt two empty dishes, and that the cook should be recompensed with the jingling of the money, as the man had been satisfied by the smell of the cook's meat. It need scarcely be said, that if the vapour from alimentary substances be capable, in any manner, of serving the purposes of nutrition, it can only be by passing into the blood-vessels of the lungs. 3. PHYSIOLOGY OF OLFACTION. In order that the sense of smell may be duly exercised, it is necessary that the emanation from an odorous body shall not only impinge upon the pituitary membrane, but that it shall do so with some degree of force. It must, in other words, be drawn in with the inspired air. Perrault and Lower found, that by making an opening into the tra The Discovery of a New World, or a Discourse tending to prove, that 'tis possible there may be another Habitable World in the Moon, with a Discourse concerning the possibility of a passage thither. Lond., 1638. 2 Holy State, London, 1640. 3 The Works of Francis Rabelais, ii. 115, Lond., 1849. In a note it is stated, "that Bocchoris, according to Plutarch, gave a similar judgment against the courtesan Tho nis, who demanded in money the price of her favours from a young spark, who had enjoyed them in imagination only." Ess. de Phys., iii. 29. 5 Needham, de Format. Fotûs, p. 165; and Haller, edit. cit., v. 173. chea of animals, and preventing the inspired air from passing through the nasal fossæ, smell was not effected; and that dogs, which were the subjects of the experiment, readily ate food they had previously refused. These experiments were repeated by Professor Chaussier, and with like results. They explain why we use effort to draw in air loaded with an odour that is agreeable to us; and, on the contrary, arrest the respiration, or make it pass entirely through the mouth when odours are disagreeable. Still they are occasionally so diffusible and expansible, that they reach, notwithstanding, the olfactory membrane; and we are compelled to shut them off by calling in the aid of the upper extremity. The air being the ordinary medium for the conveyance of odorous molecules, we can understand why the organ of smell should form a part of the air passages. The use of the nose is to direct the air, charged with odours, towards the upper part of the nasal fossa. Its situation is well adapted for the reception of emanations from bodies beneath it, and its appropriate muscles allow the nostrils to be more or less expanded or contracted. These uses assigned to the nose are demonstrated by the fact, that they, whose noses are deformed-especially the flat-nosed-or whose nostrils are directed forwards, instead of downwards, have commonly the sense feebly developed. The loss of the nose, too, either by accident or disease, has been found to destroy the sense completely; and by no means the least advantage of the rhinoplastic operation is the enjoyment afforded by the improvement of this sense. M. Béclard affirms, that an artificial nose, formed of paper or other appropriate materials, is sufficient to restore it, so long as the substitute is attached. It is proper to remark, however, that in a case which fell under the author's observation, although the nose had been lost by syphilis, the smell persisted; and two cases of a similar kind occurred to M. P. H. Bérard.3 The mode in which olfaction is effected appears to be as follows:The inspired air, loaded with odorous particles, traverses the nasal fossæ; and, in its passage, comes in contact with the pituitary membrane, through the medium of the nasal mucus. The use of this mucus seems to be, not only to keep the organ properly lubricated, but to arrest the particles as they pass,-not by any chemical attraction, but in a mechanical manner. The olfactory nerves being distributed on the membrane, receive the impression of the molecules, and, in this manner, sensation is accomplished. The use of the different spongy or turbinated bones would seem to be to enlarge the olfactory surface. According to some, however, they form channels to direct the air towards the openings of the sinuses. The sinuses, themselves, afford subjects for physiological discussion. By many they are considered to add to the extent of olfactory surface: by others, to furnish the nasal mucus. No hesitation would be felt in pronouncing both the spongy bones and sinuses to be useful in olfaction, were it not that the olfactory nerves or first pair have not been traced on the pituitary membrane covering the middle and inferior spongy Adelon, op. cit., i. 335. 2 Magendie, Précis Elémentaire, 2de édit., i. 136, Paris, 1825. bones, or on that lining the different sinuses;-that the sinuses are wanting in the infant, which, notwithstanding, appreciates odours;— that they exist only in the mammalia;-and that experiments would seem to show, that the upper part of the olfactory organ is more particularly destined for the function, and that the sinuses, which, as well as the membrane covering the middle and lower spongy bones, are supplied by filaments from the fifth pair of nerves, are not sensible to odours. Messrs. Todd and Bowman'-from the fact, that on the septum narium and turbinated bones bounding the direct passage from the nostrils to the throat, the lining membrane is rendered thick and spongy by the presence of ample and capacious submucous plexuses of both arteries and veins, of which the latter are by far the larger and more tortuous -surmise, and Dr. Carpenter2 thinks, with much probability, that the chief use of these may be to impart warmth to the air, before it enters the proper olfactive portion of the cavity; as well as to afford a copious supply of moisture, which may be exhaled by the abundant glandulæ seated in the membrane. "The remarkable complexity of the lower turbinated bones in animals with active scent, without any ascertained distribution of the olfactory nerves upon them, has"-they remark"given countenance to the supposition, that the fifth pair may possess some olfactory endowment, and seems not to have been explained by those who rejected that idea. If considered as accessory to the perfection of the sense in the way above alluded to, this striking arrangement will be found consistent with the view, which thus limits the power of smell to the first pair of nerves." That the upper part of the nasal fossa is the great seat of smell is proved by the facts referred to regarding the uses of the nose. Dessault mentions the case of a young female, who had a fistula in the frontal sinuses, and who could not perceive an odorous substance, when presented at the orifice of the fistula, because there was no communication with the proper portion of the nasal fossæ, although she was capable of breathing through the opening. M. Deschamps, the younger, relates the case of a man, who had a fistula of the frontal sinus, through which ether might be injected without its odour being appreciated, provided all communication had been previously cut off between the sinus and the upper part of the nasal fossa; but if this precaution had not been taken, the sense was more vivid, when the odours passed through the fistulous opening, than when they reached the organ by the ordinary channel. Again;-M. Richerand3 found that highly odoriferous injections, thrown through a fistulous opening in the maxillary sinus or antrum of Highmore, produced no olfactory sensation whatever. All these facts would seem to lead to the belief, that the upper part of the nasal fossæ, on which the first pair or olfactory nerves are distributed, is the chief seat of olfaction, and that the inferior portions of these fossæ, as well as the different sinuses communicating with them, are not primarily concerned in the function; but, doubtless, offer secondary advantages of no little importance. This conclusion would, Physiological Anatomy and Physiology of Man, ii. 3. 2 Art. Smell, Cyclop. of Anat. and Physiol., pt. xxxvi. p. 694, Lond., June, 1849. Elémens de Physiologie, édit. 13ème par Bérard, p. 202, Bruxelles, 1837. however, seem to admit, what is not by any means universally admitted, that the olfactory is the sole or chief nerve of smell. Especially difficult is it to embrace this view, and not to believe that the spongy bones and sinuses on which the fifth pair are distributed, are agents in perfecting the sense, when we find them so largely developed in animals that possess unusual delicacy of smell, as the dog and elephant. It has already been remarked, that the ancients believed the olfactory nerves to be canals for conveying away the pituita or phlegm from the brain. Diemerbroeck, also, maintained this view. At the early part of the last century, however, the olfactory was supposed to be the proper nerve of smell, and the opinion prevailed, with few dissentient voices, until within the last few years. Inspection of the origin and distribution of the nerve seems to indicate it as admirably adapted for special sensibility connected with smell. It is largely developed in animals in proportion to their acuteness of the sense, and is distributed on the very part of the pituitary membrane to which it is necessary to direct air, loaded with odorous emanations, in order that they may be appreciated. M. Magendie' has, however, endeavoured to show by experiment, that the sense of smell is in no wise, or little, dependent upon the olfactory nerve, but upon branches of the fifth pair. Prior to the institution of his experiments, he had observed with astonishment, that after he had removed the cerebral hemispheres, with the olfactory nerves of animals, they still preserved this sense. He had noticed, too, that it continued in lunatics, who had fallen into a state of stupor, and in whom the substance of the brain appeared, on dissection, greatly disorganized. These facts induced him to expose the olfactory nerves on living animals, and to experiment upon them; and he found, in the first place, that the nerves were insensible to puncture, pressure, and the contact of the most odorous substances. He afterwards satisfied himself, that after their division the pituitary membrane not only preserved its general sensibility, appreciated the contact of bodies, but also, strong odours, those of ammonia, acetic acid, oil of lavender, Dippel's oil, &c. On the other hand, having divided the fifth pair of nerves within the cranium, and left the olfactory nerves entire, he remarked, that the pituitary membrane had lost its general sensibility; was no longer sensible to contact of any kind; and had lost the power of appreciating odours. From these experiments, he considered himself justified in inferring, that the olfactory nerve does not preside over the general sensibility of the nose; that it has, at the most, a special sensibility as concerns odours; and that if the olfactory be the nerve of smell, it requires the influence of the fifth pair, in order that it may act. Lastly; he asks, may not the general and special sensibility be comprised in the same nerve in the sense of smell, as they are in that of taste;-in the fifth pair? These experiments are interesting; but they by no means establish, that the fifth pair is the olfactory nerve. The numerous facts, already mentioned, attract us irresistibly to the first pair or olfactory, as they have been exclusively called. It has been already remarked, that the Anatome Corporis Humani, lib. iii. cap. 8, Ultraject., 1672. 2 Précis Elémentaire, 2de édit., i. 132. 46* fifth is concerned in all the facial senses; that it conveys to them general sensibility or feeling; and that some of them are unquestionably supplied with nerves of special sensibility;-the eye with the optic; and the ear with the auditory; but that neither perhaps can fully exert its special functions, without the integrity of the fifth. The olfactory nerve is probably in this category,-is the nerve of special sensibility. It is true, that in the experiments of M. Magendie the animal appeared to be affected by odorous substances, after the division of the first pair; but a source of fallacy existed here, in discriminating accurately between the general and special sensibility. Some of the substances employed were better adapted for eliciting the former than the latter;-ammonia and acetic acid, for example. In a case before referred to, whilst the olfactory nerve was paralyzed and smell proper was wholly lost, the person was able to appreciate the contact of pungent substances; and the application of snuff to the Schneiderian membrane occasioned sneezing, because the ramifications of the nerve of the fifth pair or nerve of general sensibility were unaffected. 1 The immediate function of the sense of smell is to appreciate odours. In this it cannot be supplied by any other sense. The function is instinctive; requires no education; and is exerted as soon as the parts have attained the necessary degree of developement. In many respects the sense is intimately connected with that of taste; and the impres sions made upon each are frequently confounded. In the nutritive function, the smell serves as a kind of advanced guard or sentinel to the taste; and warns us of the disagreeable or agreeble nature of the aliment; but if a substance repugnant to the smell be agreeable to the taste, the smell soon loses its aversion, or at least becomes less disagreeably impressed. The smell is not, however, in man so useful as a sentinel to the taste, as it is to animals: there are many bodies, those containing prussic acid for example, which are extremely pleasing by the odours they exhale, and yet are noxious to man. In the animal kingdom, this sense is greatly depended upon, and is rarely a fallacious guide. It enables animals to make the proper selection of the noxious from the innocent;-the alimentary from that which is devoid of nutri. ment; the agreeable from the disagreeable; and the power appears to be instinctive or dependent upon inappreciable varieties of structure in the organs concerned in olfaction. As an intellectual sense, smell is not entitled to a higher rank than taste. Its mediate functions are very limited. It enables the chemist, mineralogist, and perfumer, to discriminate bodies from each other. We can, likewise, by it form a slight-but only a slight-idea regarding the distance and direction of bodies, owing to the greater intensity of odours near an odorous body, than at a distance from it. Under ordinary circumstances, the information of this kind derived by olfaction is inconsiderable; but in the blind; and in the savage, who is accustomed to exercise all his external senses more than the civilized, its sphere of utility and accuracy is largely augmented. Of this we shall have to speak presently. We find it, too, surprisingly developed Page 710. |