the action of the body, the change in the construction of the organ is accompanied with a change in the arrangement of the nerves. Accordingly a distinct class of nerves is appropriated in the human frame to the organ of respiration, called the respiratory nerves. Sir Charles Bell, made a very careful examination of the nerves arising from the medulla oblongata, and found that they were all distributed to those parts, which together, form the organ of respiration. The portiodura is sent to the nostrils and mouth; and to the exterior orifices of the tube which leads to the lungs. The glosso-pharyngeol, goes to the posterior openings of the nostrils, and to the upper part of the windpipe. The superior and inferior laryngeal nerves, branches of the Par vagum, supply the larynx, which is the organ of voice. The Par vagum then descends into the chest, and is distributed chiefly to the windpipe and lungs; but branches of it extend to the heart. The spinal accessory nerve is sent to the muscles of the shoulders and neck, which combine with those of the chest, in dilating the lungs. This mechanism is very different from that found in lower animals and the reason is obvious. In the lower classes of animals, the organ is limited to one function, that of oxygenating the blood; while in man, it becomes the organ of voice and the instrument of articulate language. To regulate the action of the superadded mechanism, a new and distinct class of nerves become necessary. Something certainly, which must have been provided and adapted to their office, by a wisdom above the animal organism. By studying the nature of the respiratory organ it will be seen that these new and distinct nerves are indispensible to man; but that they are not necessary in the organization of the lower animals. The first essential thing is, says Mr. Shaw, that the air for oxygenating the blood be received into a closed cavity, communicating with the external atmosphere by a single tube; the second is, that this cavity be capable of contracting on the volume of air within, so as to expel it along the tube with sufficient force to produce sound. But this formation is not found in animals. No traces of a true chest and windpipe are found below the class vertabrata. In the lower animals, there is neither circulating system or distinct respiratory organ. The first or lowest animal respiratory organ is merely a few prolongations of the integument of the animal in the shape of turfts or fringes, which float in the water, and thus expose the blood to the oxygen contained in that element. The Polype, is an example of this organism. The next formation of this organ is in the shape of small sacs within the animal, in which the integument is folded inward upon itself. The apparatus in many insects is a modification of this structure. Ranged regularly along the sides of their bodies, there is a succession of holes which are the openings of a series of small tubes which extend through their interior, by which means the air communicates with the blood. The next organization is that of the branchial or gills found in fish. In fish, we first find the mouth connected with the respiratory organ. This connection requires a new organization to expand and compress the chest, that the air may be received into and expelled from the chest. As we advance in the scale of organisms we find, as in the mammalia, a new apparatus; the diaphragm, a partition between the abdominal and thoracic cavities, stretching across from the lower border of the ribs on one side to the other. The diaphragm circumscribes the space for containing the lungs, and thereby gives greater force to the expansion and contraction of those organs; and acts as a powerful muscle of respiration in dilating the area of the chest. It is thus by the combined and harmonious action of these new and distinct nerves and organs, that man is enabled to produce vocal sounds and articulate language The respiratory mechanism of man corresponds with his superior endowments; supplying him as it does, with an organ adapted to the great purposes of communicating thought and evolving the powers of his mind; the attribute by which he holds his exalted position in creation. According to Plato, in his Protagoras, the ignorance of Epimetheus would have left man naked and unshod, unbedded and unarmed,' had it not been for the kindness of Prometheus, who stole the artificial wisdom of Vulcan and Minerva for him,which, together with fire, gave him a divine condition; and enabled him to protect himself from the severity of the seasons and the ferocity of beasts. But he was not entirely superior, until he had learned to articulate sounds and words, and had received the gifts of 'Shame and Justice,' from Hermes, the authorized agent of Jupiter. Having been led in our view of the respiratory organ, to notice the adaptations of the nerves, we will be excused for devoting a moment more to that subject. The circulating system is affected also, by the superadded mechanism of the higher animals. As the respiratory organ approaches the perfection which it attains in man, the blood vessels are divided into two distinct systems; the one for purifying the blood, and the other for distributing it over the body. Some of the most beautiful adaptations in the human system, are connected with the circulation of the blood. As the act of respiration, momentarily obstructs the flow of blood into the veins, if it be strong, regurgitation may be the result. It is obvious from this, that the veins may become congested; and be in great danger of serious injury. The veins of the head leading to the brain and eyes, are protected from these dangers, by an arrangement of the muscles of the neck, which cover and protect them. These muscles combine in sympathy with the movements of the chest, so as to compress the veins where there is a tendency to regurgitation; and to remove the pressure where the chest is expanded. The orbicularis, which covers the eye, is a part of the same provision. It compresses the eye-ball when the chest is violently contracted; by which means the veins at the back of the orbit are closed, preventing engorgement of the fine branches which ramify on the delicate coats within. This is a distinct provision to protect the eye from danger of engorgement by violent respiration; for this muscle is not found in animals, where the respiratory organ acts feebly. There is a second beautiful arrangement to protect this delicate organ from engorgement or violent circulation. The veins which ramify in the interior of the organ, between the delicate membranes that support the retina, make a circular sweep previous to entering its principal vein. This is an admirable structure for breaking the force of a retrograde current of blood, and gradually diffusing it over the mem brane. But we return to the differences in the respiration of the two kingdoms, which appear more distinctly in the action and result than in the formation of the organ itself. In our paper on 'Physical Geography" we referred to the various agents employed in the economy of nature in supplying the constant demand for carbonic acid; among which we spoke of the office performed by the animal kingdom. We therefore refer to that article for facts which we will not repeat. Animals are constantly throwing off carbonic acid, indispensibly necessary to vegetables; while the vegetable kingdom supplies animals with oxygen, alike important to their existence, thus making an exchange, and contributing to the life and growth of each other. There appears little or no analogy between the two kingdoms in the actions of nutrition and respiration, and certainly none can be found in the organic apparatus which performs these functions. As we have just seen, the different products which result from their action are so combined, that they make continual interchanges, by which they secure a counterbalance and maintain an admirable equilibrium in the midst of the disorder, which seems inevitable, but which is never permitted in the harmonious actions of nature. This is one instance only of the many to which we might refer, proving the adaptation of the various parts of Nature's complex machinery. Reciprocity, mutual exchange between the various members, is one of the first laws of life, written upon matter by the stern hand of Necessity. But in its operation we find all that is beautiful to the eye and dear to the heart. This connecting link, running through the whole of created matter, binding each separate organism and all the primordial elements in relations of dependency, is not only the triple tie of nature, but the beginning and source of innumerable blessings. Through it strength becomes the protection of weakness; age of infancy; and wisdom and purity are driven to the rescue of ignorance and corruption. The beautiful and tender relations of the domestic circle, and all the ties and obligations of society, depend upon and result from this law. So in nature, the mountain uses its elevation in collecting the moisture from the clouds, to pour it down upon the valleys, in the form of rain. The distant portions of the earth are forced into exchange by the diversity of climate; while the oceans, by which they are separated, furnish the best means for knitting them together by the ties of commercial reciprocity. While the various organisms do not spring from each other, they are bound to each other in the most intimate relations, by an unalterable law, which is both the means of their continued existence and the foundation of their happiness. He only who is unable to discover the grandeur and beauty of the relation, and the wisdom of the great PRIMARY CAUSE, is without the mighty circle, cheered by the presence and warmed by the goodness of the CREATOR, and is not likely to share its ultimate blessings. "O NATURE! all-sufficient over all, Enrich me with the knowledge of thy works; Show me; their motions, periods, and their laws, The varied scene of quick, compounded thought.' |