or lobular pneumonia, or broncho-pneumonia, is the common form of inflammation of the lung met with in infancy, and is frequently seen in early childhood. The disease is quite distinct from the croupous form previously described, differing from it in its pathology, its symptoms, and its tendency to end in death. Catarrhal pneumonia is nearly always a secondary affection, and results from spread of inflammation from the bronchial mucous membrane to the alveoli. Consequently, the disease invariably attacks both lungs, although it may be more extensive on one side of the body than on the other.
Causation.—As broncho-pneumonia is always preceded by pulmonary catarrh, .the causes which induce bronchitis in the child may be looked upon as tending in a great measure to set up catarrhal pneumonia in the air-vesicles. These are especially cold and clamp, and the inhalation of dust and other irritating particles in the air.
A severe bronchitis in the young child always inclines to spread to the finer tubes and air-cells ; but certain forms of illness have great influence in determining the extension of the inflammation. Thus, measles and whooping-cough number lobular pneumonia amongst their most frequent sequelEe, and the disease is also common as a secondary consequence of -diphtheria. In scrofulous and tubercular subjects, and even in children who are merely weakly and under-nourished, lobular pneumonia is readily excited. Therefore any influence which diminishes the resisting power of the child and lowers his general health must be looked upon as a predis posing cause of the complaint. Thus, bad feeding, insanitary conditions, and depressing derangement or disease may all help to induce this form of pneumonia. It is very common in the case of young children for the illness to be preceded by a history of more or less persistent diarrhoea. A young child who is subject to attacks of intestinal catarrh becomes excessively sensitive to chills, and after a time acquires a catarrhal propen sity which, combined with the weakness induced by the digestive went, is likely to result in an attack of catarrhal pneumonia. Neglected
colds on the chest may set up bronchopneumonia in the most robust subjects ;•but amongst the well-to-do classes it is comparatively rare to find this disease in children who are not strumous or delicate, or rickety, or who have not been lately suffering from an attack of measles or whooping cough.
Morbid Anatomy.—Lobular pneumonia may arise as a consequence of direct extension of the inflammation from the larger tubes to the smaller, and thence to the air-cells ; or may occur secondarily to collapse of the lung. In the infant the latter is the method in which the disease usually originates, for in such young subjects, on account of the narrowing of the bronchial tubes, the feeble inspiratory power, and the normal softness and compressibility of the chest-walls, collapse of the lung is a very common consequence of pulmonary catarrh. The special tendency of rickets to be complicated by bronchitis and catarrhal pneumonia has been elsewhere referred to. The difficulty of expanding the chest in this disease, owing to the softening of the ribs, greatly contributes to setting up collapse of the lung ; and any additional impediment, such as a catarrhal state of the bronchial membrane, promotes the exhaustion of the air-cells. Collapse of the lung is followed by congestion of the small vessels, owing to the impediment created by imperfect aeration of the blood, and to the absence of the expansion and contraction of the air-cells, whose movement in a state of health materially advances the pulmonary circulation. As a result of congestion of vessels there is oedema which causes great diminution in the consistence and cohesion of the tissue at the affected spot. In this state the part is ready for the development of inflammatory changes. Inflam mation readily extends to it from the air-tubes ; or the irritation induced by the penetration into it of secretion from the bronchial mucous mem brane excites the inflammatory process.