The geologic history of China and its influence upon the Chinese people / by Eliot Blackwelder.

  • Blackwelder, Eliot, 1880-1969.
Date:
1914
Catalogue details

Licence: In copyright

Credit: The geologic history of China and its influence upon the Chinese people / by Eliot Blackwelder. Source: Wellcome Collection.

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    GROUP 4-PHYSIOLOaY & HEALTH • THE BODY & ITS MAINTENANCE-CHAPTER 29 The Breathing Apparatus. Chemical Changes in the Breath. Chest Expansion and Mobility. Methods of Breathing. HOW TO WE will now briefly consider the nniscular and chemical aspects of ros]iiration. Respiration is essentially a chemical com- bination of oxygen with the tissues, resulting in oxidation, followed by the surrender of a volume of earbon dioxide about equal to the volume of the oxygen combined. In the lowest and smallest organisms the oxygen is taken in all over the general surface of the body, but in the higher and larger organisms there is a specialised apparatus to facilitate the intake of oxygen and the output of carbon dioxide. A small unicellular organism can absorb oxygen from its general surface. A fish requires gills and a system of canals, while the mammals require lungs, thoracic muscles, and a system of canals. The Breathing Apparatus. The breathing apparatus in man consists briefly of mouth, nose, pharyirx, laiynx, trachea, lungs, thoracic muscles, and the whole vascular sy'^stem. The larynx, or voice-box, leads into the trachea, or windpipe, and the windpipe divides into two big branches called the right bronchus and the left bronchus, which go to the right and left lung respectively. The bronchi, in turn, bifurcate into smaller and smaller branches, and when the branches have reached almost microscopic dimensions they expand into little, elongated sacs known as infundibula, which are dimpled with little depressions known as air-cells. . Looked at from the exterior, the infundibula, with their little, bulging air-cells, look like bunches of grapes. Over the air-cells arc fine blood-vessels, and the infundibula w'ith their blood-vessels are bound together by a fine clastic stringy substance into the lobules of the lungs. The lungs therefore consist mainly of tine branching tubes, ter- minating in air-cells, together with a mcshw'ork of arteries, veins, and capillaries. The object of all this branching is to provide a large surface where the oxygen of the air inspired into the air-cells may come into close contact with the red blood - cells of the blood. It has becur calculated that there are over seven hundred million air-cells in the average lungs, with a total surface of about 90 square metres. The lungs are contained in the case of bone and mu.scle known as the chest, or thorax. The walls of the thorax are formed by the breast- bone and ribs with intercostal and other muscles, and its floor is formed of a strong sheet of muscle and fibrous tissue know'ii as the diaphragm, w'hich separates the cavity of the chest from the cavity of the abdomen. Retween the lungs is the heart. This, as briefly as ])ossible, is the respiratory ap|)aratus, and now we w'ill glance at its mode of w'ork. How the Lungs are Inflated, It is (piite commonly believed that we inflate the BREATHE lungs, and that the lungs lift the chest wall, but the reverse is the case. In slang, the chest is often spoken of as the “ bellow'S,” and the slang has truth in it, for it enlarges like a bellows or accordion, and as it enlarges it sucks air through the nose and mouth into the air-cells and thus inflates the lung. The enlargement of the chest cavity is effected partly by the intercostal muscles and by other muscles which raise the ribs and breast-bone, and partly by the strong diaphragm muscle. The muscles that expand the thoracic cavity relax, and the chest cavity is contracted again owing to the elasticity of the lungs, the weight of the ribs, and the contractile influence of a few muscles. The movement of the muscles that expand and contract the chest cavity is usually reflex, and is under the command of a nerve centre at the top of the spinal cord ; and the rate and depth of the breathing is regulated according to the requirements of the system by messages sent to the nerve centre from the lung and skin and other jiarts. Thus a cold douche ina} take our breath away, and a little excess of carbon dioxide in the blood may quicken respiration, but the wall, as we know', has also a certain amount of control over the breathing. Chemical Changes Made by Breath= ing. The air, then, in this manner is inspired and expired. In the inspired air is the oxygen, and the oxygen, according to certain laws, is taken u]5 by the blood and red blood-celLs, and carried round the body, to be added to various tissues and unlock their energy. In the expired air is a large quantity of carbon dioxide which has been formed by the oxidation of tissues all over the body, and has been carried to the lungs by the circulation. The breathing thus brings oxygen to the tissues and helps to remove the debris of tissues. Hence, during active exercise the breathing is (juickcr, so as to provide more oxygen and remove more carbon dioxide. A Chemical Measure of Energy. It has been found experimentally that a man discharges |)t'r minute Ifll'O cubic ccutimctrcs of carbon dioxide when a.slec}); 5t)9 cubic centi- metres when walking at a rate of two miles an hour ; S.'il -2 cubic centimetres when he is walk- ing at a rate of three miles an hour; and 1581'9 cubic centimetres when walking a treadmill. It has been found, too, that horses discharge twice as much carbon dioxide when trotting as when w'alking. The amount of carbon dioxide is therefore a nu'asure of energy, and the most acti\c and warm-blooded animals discharge the most carbon dioxide in })ro]iortion to their weight. Men. it may be noted, di.schargc considerably more carbon dioxide than women. The expired breath carries away from the THIS GROUP EMBRACES ANATOMY, PHYSIOLOGY, AND HYGIENE ;{G54