Another mechanical means by which the force of the inspiratory act may be interfered with is deficient rigidity of the chest-wall. Abnormal softening of the ribs is a very important agent in the production of col lapse, and the frequency and danger of the lesion in rickety subjects is mainly owing to this simple cause. The parieties of the chest in the infant are naturally more flexible than they are in the adult. Even when the ribs and their cartilages are perfectly sound, considerable recession of the lower ribs may be seen at each inspiration if an impediment exist at any part of the air-passages to .interfere with the ready entrance of air into the lung. If the ribs are softened, as in rickets, the same recession is noticed although the passages may be perfectly free ; for the softened ribs cannot resist the pressure of the atmosphere, and the force of the inspired air is insufficient by itself to prevent the thoracic parieties, where least supported, from sinking in. Consequently in this disease the lower lobe's of the lungs are very insufficiently filled with air. If such a child suffer from pulmonary catarrh, the additional obstacle to efficient inspiration created by the mucus in the tubes may lead to complete collapse of the inferior parts of the lungs. On account of the mechanism by which it is produced, collapse of the lung must always be a secondary lesion. It is found as a complication of various forms of illness. Diseases of which pulmonary catarrh is a common symptom, as whooping-cough and measles ; diseases which interfere directly with the passage of air through the glottis, as diphtheria, laryngitis stridulosa, post-pharyngeal and other abscesses in the neighbourhood of the larynx ; diseases which diminish the force of the inspiratory act, either by mechanical opposition as in abdominal tumours and rickets, or by im pairing the muscular strength of the patient—in all these cases collapse of the lung is liable to be found.
Morbid Anatomy.—The extent of the collapsed area is in proportion to the calibre of the tube at the point of obstruction. According, therefore, as the lesion involves many lobules over a considerable surface, or is limited to a few, the collapse is said to be diffused or lobular. The airless part of the lung is shrunken and therefore depressed. It is purple in colour and to the touch feels soft and dense. It does not crepitate. On section the surface is smooth, and blood or bloody serum exudes on press ure. Around the collapsed portion the air-cells are emphysematous.
Lobular collapse is often situated at the anterior edges of the lungs, but may occupy any other parts. The diffused variety is most common at the posterior surface, but may be seen elsewhere. It penetrates for a variable distance into the organ, and sometimes an entire lobe or even the greater part of the lung may be found shrunken and airless. After death, if the lesion be recent, the collapsed tissue can be completely reinflated through the bronchus.
Symptoms.—The symptoms are found to vary considerably in different cases according to the extent of the collapse and the degree of strength of the patient. In a very weakly infant rapid and extensive collapse is often a cause of sudden death. In such cases the preliminary catarrh is not
necessarily severe. Often, indeed, it is trifling ; and the rapidity with which death occurs gives rise to much surprise and consternation. The impaction in a large bronchus of a single plug of mucus may be thus fol lowed in a young and feeble subject by rapidly fatal consequences. An other common result of the lesion is a convulsive seizure ; and sometimes the fits succeed one another with great rapidity, each attack increasing the exhaustion of the patient and aggravating the pulmonary mischief until death ensues. These cases are not, however, always immediately fatal. In a sensitive child collapse of comparatively limited extent, if it occur suddenly, may give rise to an eclamptic seizure ; but this may not be re peated, and perhaps by judicious and energetic treatment the child's life may be saved.
Such severe symptoms are, however, exceptional. In most cases the occurrence of collapse is indicated by less striking phenomena. A weakly infant is suffering from the ordinary symptoms of bronchial catarrh. He -coughs more or less loosely and his breathing is moderately hurried, but there is nothing to excite apprehension. Suddenly, however, a change oc curs. The child becomes restless and evidently distressed ; his face gets distinctly livid, especially about the eyelids and mouth ; his breathing, which had been more laboured than natural, increases in rapidity but di minishes in depth ; the cough ceases or is feeble and faint ; and the inter nal temperature of the body is found to be below the level of health.
The face usually indicates profound depression. The features look pinched ; the eyes are dull and hollow ; and the forehead is often moist with a cool, clammy perspiration. The naves act in respiration, and the breathing is very rapid. The number of respirations commonly reaches 70 or 80 in the minute, and the perversion of the pulse-respiration ratio is extreme. In very young infants the breathing is usually very shallow, with little movement of the chest-walls ; but in infants eight or nine months old, whose ribs are softened by rickets, the bases of the chest sink in to some extent at each inspiratory movement. The child refuses to suck and often seems to have difficulty in swallowing, so that he can hardly be persuaded to take milk from a spoon.
The physical signs, if any are to be discovered, consist in slight dul ness at the posterior base of one lung, or extending upwards in a narrow vertical strip at each side of the spine. The dulness can often only be discovered by very gentle percussion, as a sharp blow with the finger brings out the resonance from healthy tissue underlying the condensed layer. The breathing conducted from healthy tissue around is of bronchial quality, and may be weak or fairly loud, according to the strength of the respiratory movement. Vocal resonance is usually annulled. Sometimes coarse crep itation is heard at the confines of the collapsed area. These signs are only to be discovered when the lesion is of the diffused variety. In lobular col lapse any dulness which may be occasioned by the presence of the solidi fied patches is neutralised by the compensatory emphysema set up in their neighbourhood.