General Introduction. The function of respiration implies access of air to the blood and of blood to the air, a double mechanism. Respiratory movements-effected by nerve centres. Pulmonary circulation. 1. Dyspnoea arises (a) from insufficient access of air, and (b) from inefficiency of the pulmonary circulation. Compensation of dyspnoea, generally insufficient and liable to-fail. 2. Asphyxia, the phenomena of sudden suffocation. Ecchymoses in pericardium, pleura, and lungs the most obvious visible results post mortem.

A. - The Nasal Passages. 1. Congenital malformations; 2. Haemorrhage; 3. Acute catarrh; 4. Chronic catarrh; 5. Syphilis and tuberculosis; 6. Tumours; 7. Foreign bodies.

B. - Larynx and Trachea. I. Malformations. II. Inflammations. 1. Diphtheria: 2. Acute catarrh, sometimes leading to oedema glottidis; 3. Chronic catarrh 4. Subglottic inflammation; 5. Inflammation of cartilages. III. Syphilis and Tuberculosis. IV. Tumours and Foreign bodies.

C. - The Bronchial Tubes. Introduction. I. Inflammations. 1. Bronchial catarrh r constituting ordinary bronchitis, (a) acute, (b) chronic; 2. Septic bronchitis; 3. Fibrinous bronchitis. II. Stenosis and Dilatation. 1. Narrowing; 2. Dilatation; bronchiectasis. III. Tumours and Foreign bodies. Importance of the lesions resulting from foreign bodies.

General Introduction

IN studying the different diseases of the respiratory organs it is-proper to consider the effects which they have on the functions of the organs concerned. In this introductory section the structure and function of the organs will be considered together with the alterations in function to which disease gives rise.

The respiratory organs are designed to bring the air into close relation with the blood in order to an interchange of gases between the two. With this in view there is a double mechanism by which, on the one hand the air is carried into the lungs, and on the other the blood is propelled into the pulmonary capillaries. Both of these processes are equally necessary to the performance of the respiratory function, and the latter is deranged by interference with either of them.

The respiratory organs proper are concerned primarily in the admission of air into the lung alveoli or air-vesicles, where it comes into close relation with the blood. The air passes through the nose or mouth, into the larynx, thence down the trachea and bronchi till it reaches the lung alveoli, where the essential respiratory surface exists. The pulmonary capillaries ramify in a very abundant plexus in the walls of the lung alveoli, and the blood is separated from the air merely by the capillary wall and a single layer of very thin epithelium. It is here that the blood gives up its excess of carbonic acid and absorbs oxygen, the haemoglobin of the red corpuscles being the medium of this interchange. The blood circulates through the capillaries with great rapidity, but the interchange of gases occurs in the brief period occupied by the corpuscles in traversing their respective capillaries.

The respiratory movements, by which the air is alternately carried into the lungs and expelled from them, are effected partly by muscular effort and partly by elastic recoil. The movements of inspiration are purely muscular, whilst those of expiration are, under normal circumstances, for the most part mechanical, due to the elasticity of the lung tissue and the natural sinking of the sternum and ribs by their weight and elasticity. But even under normal conditions expiration is often assisted by muscular effort, as in all forced or rapid expirations. Like all muscular movements those of respiration are under the control of the nervous system.

The respiratory centres are situated in the medulla oblongata. These centres, removed as they are from the lungs, are influenced in their action by the condition of the blood. An excess of carbonic acid or a deficiency in oxygen in the blood reaching the centres at once stimulates them to increased action. As all muscular actions and other tissue processes cause a consumption of oxygen and a liberation of carbonic acid, the amount of these in the blood varies from time to time. These varying amounts influence the respiratory centres, so that, during active exertion, for example, when oxygen is abundantly absorbed and carbonic acid given off by the muscles, the respiratory movements are increased in frequency or in depth, or in both. There are thus great variations within normal limits. It is important in relation to pathological variations to remember that it is the condition tit the blood in regard to its saturation with oxygen and carbonic acid which influences the movements of respiration, and not directly any local circumstances in the respiratory organs themselves.

The pulmonary circulation is chiefly dependent on the right ventricle of the heart, whose force propels the blood into the pulmonary artery and on into the capillaries and veins. The respiratory movements also exercise an influence on the circulation. During inspiration, as the capacity of the chest is increased and the intra-thoracic pressure is diminished, the passage of blood into the expanding lungs is facilitated, whilst the passage of the blood from the lungs by the pulmonary veins is hindered. Blood will thus surge into the lungs during inspiration and be partly retained there. On the contrary, during expiration the intra-thoracic pressure is increased and the volume of the lungs diminishes. The blood coming from the right ventricle will by this be partially stayed, whilst the course of that passing onwards to the left auricle will be hastened.