THE POPULAE EDUCATOE. 



not hang together, but exert a force to fly off from one another, 

 the substance they form is called a gas. The sense of touch, 

 strictly and properly denned that is, excluding the sensation 

 of heat and of resistance has to do with solids. The sense of 

 taste has to do with liquids only, as nothing is sapid which is 

 not liquid or capable of being dissolved. The sense of smell 

 occupies itself with gases ; for these alone can gain access to 

 the organ, or cause the sensation of smell. Lest the reader 

 should suppose this statement opposed to the testimony of his 

 experience, from the well-known fact that solids, such as cedar- 

 wood, camphor, and rnnsk, excite the sensation of smell, while 

 ordinary scents are preserved and carried about in a liquid 

 form, it must be explained that these substances contain volatile 

 essential principles, which, on free exposure to the air, are slowly 

 given off in a state of vapour. Some solids give off particles 

 of their substance in a state of vapour without first becoming 

 liquid, as is ordinarily the case. Thus snow, which coats the 

 earth in winter, will diminish daily, even though the air is 

 fijosty, and there is no melting process going on. In other 

 sases, as in cedar-wood, oils naturally volatile seem to be long 

 entangled in the solid matter, and but slowly rendered to the 

 air; but their odoriferous power is so great that very small 

 portions of them produce strong perfumes. This is sometimes 

 truly wonderful. Dr. Carpenter states that a grain of musk 

 may be freely exposed to the air for ten years, during which 

 time it perfumes the whole surrounding; air; yet when weighed, 

 there is no perceptible loss observed. Matters which exhale 

 odorous emanations are detected at a great distance, from the 

 tendency of gases to pass through and diffuse themselves 

 equably throughout all other gases. Thus, though there be but 

 a very small escape of coal-gas in one part of the room, it soon 

 announces itself to the nose in every corner of the apartment. 

 This is a faculty peculiar to gases, and produces many in- 

 teresting results, which, however, cannot now be dwelt upon. 



The final cause for which the sense of smell is given to the 

 higher animals i.e., to beasts, birds, and reptiles is primarily 

 to warn them against receiving into the lungs and stomach 

 noxious matters, and secondarily to guide them in the search 

 for wholesome air and food. As a rule, to which, however, 

 there are many exceptions, nauseous smells are associated with 

 noxious gases, and that food which gives off a pleasant aroma 

 is of a nature, and in a condition, to supply good nutriment. 

 The bulk of the atmosphere consists of inodorous gases, admi- 

 rably mixed so as to suit the purposes of respiration, and the 

 main products of vegetable life are nutritive and bland ; but 

 small quantities of destructive effluvia and of deadly poisons 

 are no uncommon things in natiire, and unless some kind of 

 quarantine were exercised on air and food, the system could not 

 be maintained in health. True, therefore, to its office of 

 sanitary inspector, the organ of smell holds a position at the 

 entrance of the passages for air and food. In order to appre- 

 ciate its office it is necessary to understand the relation of these 

 passages to one another. This is best done by a reference to 

 the illustration. The largest figure represents the nose chamber 

 of the left side; the hollow of the mouth below it ; the pharynx, 

 or channel for food, running down towards the stomach on the 

 left side (of the figure) ; and the larynx, or channel of the air, 

 when pursuing its course to the lungs, parallel to it, on the 

 right-hand side, as they would appear if the head were cut in 

 two with the downward stroke of a sharp, resistless knife, made 

 as near to the middle plane as possible, yet so as to be on the 

 left of the upright partition between the two nose-chambers. 

 The ordinary course of the air, when no food is being swallowed, 

 is upward through the nostril, then horizontally through the 

 lower part of the nose-chambers, then downward and forward 

 behind the soft palate, entering the hole immediately below 

 the part marked as the " epiglottis," and so on to the lungs. 

 The simpler course of the food is horizontally through the 

 tnouth, and then vertically downward. If the reader has 

 understood the engraving, he will see that the air and food 

 passages cross one another ; or, perhaps, it makes it more clear 

 to say that the air passage enters the food canal from above, 

 and passes out again below and in front of it. This is a 

 singular arrangement, and open, one would have said, to the 

 obvious objection that the food might get into the lungs, where 

 it IB not only not wanted, but could not bo for a moment 

 endured. This catastrophe is, however, provided against by 

 the act of swallowing, in which the soft palate closes the air 



entrance above, and the epiglottis is bent down, while the sides 

 of the hole below are so contracted beneath its overhanging 

 and protecting hood, that the food passes over it, and the drink 

 on each side of it, without danger of their making an entrance 

 into the larynx. It will be seen that the effluvium from food 

 not only rises into the nasal organ when it is presented to the *. 

 mouth, but passes to it, also, after it has been introduced into 

 the mouth, so that the nose is an effective guard to this entrance, 

 as well as to that which it more immediately occupies. 



The external protecting framework, or nose, covers in tho 

 nasal chambers in front, and, on account of its oblique direction, 

 overhangs the orifices, which are further defended from intrusive 

 solids by a number of stiff hairs. At the upper part, or roof of 

 the nose, this framework is of bone, because there no flexibility 

 is required, but towards the point it is composed of cartilages, 

 which are more elastic, and which can also move in relation to 

 one another, while the outer and lower sides of the orifices are 

 composed of yet more bendable cellular tissue. These wings of 

 the nose can play up and down, and to and from, the central 

 partition by the action of muscles, so as to enlarge, contract, or 

 slightly alter the direction of the openings ; but the framework 

 is, nevertheless, stiff enough to keep the nostrils moderately 

 distended while in a state of rest. Stretching horizontally 

 backward from the nose are the nasal chambers, divided from 

 one another by a plain partition, which is bony behind and 

 gristly in front, and they pass under the chamber of the brain 

 and over the cavity of the mouth, to open backward over the 

 throat. Solid floors of bone divide this second storey of the head 

 from the upper and lower rooms, and bones also wall in the 

 right and left sides. These walls, however, are not smooth and 

 plain like the central partition, but have three bony projections 

 one above the other, which are called turbinated bones, because 

 they are curled upon themselves like scrolls, the first convex 

 surface of the scroll being directed inwards. These turbinated 

 bones stretch inwards, nearly reaching the plain partition, and 

 thus divide each lateral chamber into three horizontal passages, 

 called the upper, middle, and lower meatuses. All the interior 

 of the chambers is covered with a membrane, which is very 

 thick and pulpy on the scroll bones, the roof of the chamber,, 

 and central partition. This membrane is peculiar in that it 

 secretes a slimy mucus, it is very vascular, and so contain* 

 much blood, and the ultimate fibres of the nerve of smell lose 

 themselves in its substance. The nervous apparatus of smell 

 on each side arises from under the brain by three roots ; it is in 

 tho shape of a little round horizontal bar of brain matter, ending 

 in a bulb, and it lies in a groove of the soft brain above, and of 

 the hard bone beneath, being separated from its fellow by a 

 crest of bone. These bulbs being placed in the brain-case, send 

 down, from all along their course, through many holes in the 

 bones on which they lie, nervous cords, which divide and sub- 

 divide, and run, some to the vertical central partition, some to- 

 the top scroll-bone, and some to the roof of the chamber. Their 

 distribution, of course, indicates where the sense of smell resides, 

 that is, not in the main channel of the air, which passes along- 

 the floor of the passage, but in the upper part of the chamber. 

 Hence, when we want to smell anything, we take means to get 

 the gas driven upward into the upper part of the nose. This is 

 effected by contracting the nostrils, and drawing the air suddenly 

 and sharply in, BO that it is directed upwards instead of along 

 the floor of the passage. 



It has been remarked that the membrane of the nose is very 

 full of blood-vessels, and this is important, because the presence 

 of much warm blood, distributed over a surface purposely folded to 

 give it a greater extent, has a tendency to warm the cold air as 

 it passes through the complicated channels before it is intro- 

 duced into the lungs. That cold air, introduced through the 

 nose, instead of through the mouth, is less likely to be injurious, 

 is so far recognised, that respirators are used by delicate persons 

 in cold air, while it is not thought necessary thus to protect 

 the nose. 



There are curious connections botween the nasal chambers 

 and the hollows in many of the bones of the face and head, 

 which are analogous to the air cavities of birds' bones. The 

 nose has also another office, in that it serves as a sewer for 

 the eye. Two little ducts from the inner corner of the eye 

 join and form a tube, which, after passing through a bony canal, 

 delivers its drainage into the lower mcatus of tho nose by a, 

 small orifice, shown in the engraving. Hence, violent blowing 



