Olfactory lobe

“ Not only is most of the air breathed in through the nose and warmed in its passage through, but the nose is the organ of smell and by means of the peculiar property of its nerves protects the lungs against deleterious gases and helps the taste discriminate. The olfactory or first cranial nerves, after emerging from the brain, lie on the under surface of the frontal lobe and rest on the ethmoid bone in what is known as the olfactory tract. ”

“ We are now able to follow the undulations we term light, not only into the eye, but into the brain itself, locating their central station in the occipital lobe, whence their effects radiate all over the organism. And in the case of olfaction Pawlow has taught us that its chief vegetative function, the result of radiations from the olfactory central station in the brain, is the arousing of the digestive glands to activity. ”

“ Olfactory apparatus similar to that of fishes, viz. a small aperture near the extremity of the snout leads into a cavity or cul de sac, lined by a delicate membrane, plentifully supplied by the fibrillæ of two slender olfactory nerves, which go off from the anterior end of each lobe of the cerebrum. The brain is of an oblong figure, the cerebrum is formed of two lobes, the cerebellum of one lobe situate directly posterior, not much thicker than the medulla oblongata. ”

“ At the same time, the olfactory lobes, each containing a prolongation of the ventricle, have become much more pronounced (vide Pl. 16, figs. 4a and 4c, ol.l) . The root of the olfactory nerve is now very thick, and the ganglion cells it contains are directly prolonged into the ganglionic portion of the olfactory bulb; in consequence of which it becomes rather difficult to fix on the exact line of demarcation between the bulb and the nerve.
Stage Q is the latest period in which I have investigated the [Pg 402] development of the brain. ”

“ The waders, which have the largest olfactory nerves, are also those birds that display the greatest keenness of scent. Reptiles have very large olfactory lobes, leading us to believe that they discern odors readily, but at present we know little of the impressions they are sensitive to in this respect. Fish also have an olfactory membrane. Fishermen have always remarked that they may be attracted or driven off by throwing certain odorous substances into the water. ”

“ As we proceed downward, the hornlike projection of the olfactory nerves beyond the central hemispheres goes on extending more and more, and the relative magnitude of the terminal ganglia or olfactory lobes increases in similar order. ”

“ The physical theory of odour, then, refers that quality to the vibration of the molecule. It suggests that the molecules of an odorous body passing in the gaseous or, in fishes, the liquid state into the olfactory region of the nose, are there received by the film of mucus in which the olfactory hairs lie, and stimulate these hairs by their molecular vibration. No chemical change is supposed to take place, only, as it were, a mechanical stimulation, comparable to the mechanical stimulation of the retina by the waves of light. ”

“ When one odour destroys the other, the obliteration must take place in the cerebral centre. Certain odours are antagonistic, such as musk and oil of bitter almonds, volatile oils and iodoform, ammonia and acetic acid. It is not unlikely that when one odour predominates among many, this may be due not to any chemical action of one substance over another, but that the missing sensations may be accounted for by their failure to excite the olfactory region of the cerebrum in the presence of a stronger stimulus. ”

“ Gleg has estimated that the reaction time for auditory sensation is from 0’12 to 0’15 of a second, whereas the reaction time for smell is as much as 0’5 of a second, only one sensory stimulus being slower, that of pain, namely, which occupies 0’9 of a second.
Odours are conveyed to the olfactory end-organ in the air we breathe. Before they can rise into the air from the odorivector (the odorous body) and be transported they must, it is clear, pass into the vaporous or gaseous state. (In the case of fish, of course, the odour must undergo solution, that is pass into the liquid state.) ”

“ But almost certainly some of the air is diverted up into the olfactory region in light eddies, and the act of sniffing, which is a short inspiration abruptly begun and ended, and which we instinctively resort to when trying to detect a faint odour, is obviously of a nature to propel side-streams or eddies up into the olfactory zone. One is reminded of the production of smoke rings from a box.
We smell not only during inspiration, however, but also during expiration, the latter conveying to the olfactory region the flavours of food and drink. ”

“ The olfactory system consists of the outer nose, which projects from the face, and the nasal cavities, contained in the skull, which support the olfactory mucous membrane for the perception of smell in their upper parts, and act as respiratory passages below. ”

“ We should be guilty of error, however, were we to conclude that the scantiness of olfactory names is due to the lack of recognition by the consciousness of early man of smell in general, or to a failure to distinguish between different odours, because savages, in general less discriminating and analytical than cultured races, have, there is every reason to believe, a more acute and highly perfected olfactory sense. ”

“ By cutting away the cartilage dorsal to the nasal sac its base will be exposed, and the olfactory bulb will be shown to be closely adherent to a considerable part of the postero-dorsal surface of the organ. Numerous short nerves can be demonstrated to pass from the olfactory bulb into the olfactory organ; all these nerves together are considered as the first cranial or olfactory nerve. ”

“ In the macrosmatic terrestrial animals not only is the olfactory sense relatively highly organised, but it is absolutely the predominant sense. Vision is subsidiary to it. In their brains the olfactory region constitutes by far the largest component. (The same, by the way, is true of the Reptilia.)
In other words, it is upon the olfactory sense that these animals chiefly depend for their knowledge of the world. By it they are directed to their food, warned of their enemies, and attracted to their mates. Their universe is a universe of odour. ”

“ SMELL IN FOLK-LORE, RELIGION, AND HISTORY Evidence of olfactory influences is encountered in folk-lore not infrequently, particularly in connection with primitive medicine, and survivals of old olfactory methods of treatment are still extant, not only in the doings of the wise women of our remoter country villages, but also, as we shall see, in modern scientific medicine. ”

“ Odors, to be perceived, must be taken up by oxygen, and borne by it to the organ of smell. In a word, odor is the odoriferous particle itself, while light is not the light-giving body.
Does oxygen exert a chemical influence on those atoms of which it robs odorous substances? We do not know, neither do we know of what kind is the action which occurs on the contact of odor with the olfactory nerve, whether the phenomenon is a mere mechanical agitation, or whether some chemical decomposition takes place in the case. ”

“ Olfactory cells in man are only found in the upper—the olfactory—region of the nose, spread over a surface of about one square inch, the olfactory area—part lying on the outer (lateral) wall of each nasal passage and part on the septum, or partition between the nasal passages. In macrosmatic animals the olfactory area is relatively greater than in man, but there is apparently no other difference between them. ”

“ A recent development of the theory which we owe to Heyninx, a Belgian scientist, brings the process very closely into harmony with what 122occurs in the eye. According to this authority, olfaction is in reality a perception of ethereal undulations of the same character as the undulations of light, these undulations being provoked by the intra-molecular vibrations of the odorous vapour in the nasal mucus and transmitted to the olfactory hairs not by immediate contact, but through the medium of the ether. ”

“ The sense of smell depends upon the contact of odorous emanations with the sensitive olfactory membrane, and such contact can only take place when there is a free passage for them through the nose. If the nasal membranes become thickened from any cause, thus partially or wholly preventing the passage of air, the capacity of smell is correspondingly affected. ”

“ Thus in the opening paragraph of this book we encountered a large number of olfactory words. But they are all vague ; some applying to pleasant, some to unpleasant, odours. Many of them are very expressive, for disgust begets strong language. But although our olfactory vocabulary may be forceful, it is not discriminative. In other words, it is an emotional, not an intellectual, vocabulary,
These considerations will become more obvious as we deal with olfactory epithets in detail.
Thus smells may be faint or “strong,” but so may any other sensation. ”

“ Olfaction is, indeed, one of the primitive senses of animal life. And in man, as it happens, while vision has constructed for itself a highly complicated camera-like end-organ, and hearing has produced an apparatus even more elaborate, the olfactory organ, on the other hand, remains primitive, its essential structure having undergone no apparent evolutionary change from the simplest and earliest type. ”

“ When the physicist can control the vibrations of his electrons and make them rotate in accordance with his will, then he may be able to synthesise new odours—till then we have no means of testing his theories.”
The older view of olfaction—and many modern scientists, as we see, still adhere to it—is that the odorous molecule acts as a chemical reagent upon the olfactory hairs. ”

“ The Olfactory Stimulus.—Only substances in the gaseous state can be smelled. From this it is inferred that the stimulus is supplied by gas particles. Solids and liquids are smelled because of the gas particles which separate from them. The substance which is smelled must be kept moving through the nostrils and made to come in direct contact with the olfactory cells. There is practically no limit to the number of distinct odors that may be recognized. ”

“ Now, the chemical irritant, in the latter case ammonia gas, affects not the olfactory nerve, but certain naked nerve fibrils in the mucous membrane belonging to what is known as the fifth cranial nerve, a nerve of simple sensation. [2] And the simultaneous irritation of the eyelids, and in the case of the pollen and horse effluvia the bronchial tubes, shows that these 95resemble in their action the simple chemical irritants, and not the odours.
2. The difference between those two sensations becomes clearly evident when an anosmic person is peeling an onion. ”