MEDICAL 2 It) Alveoli Wall with Capillaries that they can divide no more. Each tiny bronchus, therefore, expands into a little sac, or vesicle, almost like a minute balloon. All round the walls of these air sacs is a net- work of capillaries, which, as was explained in the previous article, are microscopic blood- vessels. These capillaries contain the venous blood brought from the right side of the heart by the pulmonary arteries, which divide like the bronchi into smaller and smaller arteries until they become so small as to be called " capillaries," filled with venous blood. Now imagine each little air sac, or alveolus, filled with pure air, which has passed down through the air passages to the furthest extremity of the lungs. The oxygen in this air has to pass through the thin walls of the air sacs, then through the walls of the capillaries right into the blood. At the same time, the carbonic acid gas passes in the opposite direction from the blood through the capillary wall and air sac wall into the interior of the little air sac. From there it passes into the minute bronchus leading from the air sac, thence up the air passages, to be expired atmosphere. How We Breathe The process of respiration is divided into two stages ; inspiration, or drawing in of fresh air laden with oxygen, and expiration, or breathing out of foul air. When we take a breath the chest enlarges because the ribs are elevated or raised by the muscles of respiration and the diaphragm is depressed. The lungs, being practically hollow elastic bags, also expand, and air rushes in through the air passages to fill the vacuum which is produced. With every inspiration about a pint of air is carried into the lungs to mingle with the air which is already present in these organs. Inspiration is always followed by expiration, which is the forcing out of the air in the lungs by the ribs descending and the diaphragm ascending to their original position. Expired foul air contains less oxygen and more carbonic acid than inspired air, which gives up a large part of its oxygen in the lungs and gains carbonic acid from the venous blood. Expired air is also warmer and moister. When the blood in the lung capillaries loses carbonic acid and gains a new supply of oxygen, it becomes arterial blood, which is bright red in colour. This arterial blood is carried by the pulmonary veins back to the left side of the heart and is there sent to all parts of the body. All living cells require oxygen for their nourish- ment, and the oxygen is carried by the red corpuscles in the blood to every organ, every tissue, and every cell of the body. Asphyxia If the body is not getting its full supply of oxygen it gradually gets poisoned with carbonic acid gas, and a condition called asphyxia is produced. This may follow upon any obstruc- tion in the air passages, such as in choking or suffocation, when air is prevented from passing tlown the windpipe. lo the same way respira- Diagram of air sacs. The oxygen in the air which has passed down through the air passages reaches these sacs and then passes right into the blood. into the tion may be stopped by pressure on the chest walls, and people will die in a crowd from asphyxia because the chest wall is mechanically prevented from enlarging. In drowning, the water in the respiratory passages causes asphyxia because it prevents the air from entering the lungs. It is most necessary for a nurse to understand - - what respiration is, and to know something of the anatomy of the organs of respiration. One of her duties, especially if she is nursing a "lung case," is to count the respirations, to note whether they are natural or unnatural, shallow or noisy, or irregular. Normally we breathe fifteen to eighteen times per minute. In fever, the breathing is accelerated. In certain ill- nesses, such as heart disease, breathing may be difficult. In pleurisy, respiration is painful from the friction of the inflamed pleurae against each other. In the " Dictionary of Ailments " the various lung diseases will be dealt with in detail, and, in a later article, the nursing of these ailments will be dealt with practically, and full instructions given how to treat the various symptoms, such as cough, difficult breathing, pain, etc. These introductory articles dealing with physiology ought to be referred to by the nurse, in order that she may have an intelligent grasp of what is happening in the body in health and in disease. The nurse who merely treats symptoms mechanically, without knowing the reason why, is not only less useful, but may even be dangerous to the well-being of the patient. It is a good thing to know how to make a poultice for anyone who has a pain, but that sort of knowledge ought not to be the sum of the nurse's curriculum. Diseases of the Lungs The nurse who understands the simple anatomy of the lungs and air passages will, for example, be in a position to understand the difference between bronchitis, pneumonia, and pleurisy. These will be described later in detail. Meanwhile, it is sufficient to say that Bronch- itis is a catarrh, or inflammation, of the bronchial tubes, and, as is mentioned in the article on colds and catarrhs, it may spread downwards from the nose or throat. Pneumonia is an inflammation (caused by a special microbe) of the air sacs. These become solid, and in most cases the bases of the lungs are affected. Pleurisy is inflammation of the pleura covering the lungs and lining the chest walls. Phthisis, consumption, or tubercular disease of the lungs is inflammation of the lung tissue, caused by the tubercle bacillus. The nursing of phthisis will be given special notice in this series, because good nursing is essential, not only to recovery, but to the prevention of the spread of the disease. In a later article the nurse wili learn how to take the temperature, how to dis- tinguish the different types of cough, how to treat pain by poultices and fomentations, how certaii; positions help a patient to breathe more easily, To be condnHed.
