(_i_) Pneumonia is the technical term for inflammation of the lungs or _lung fever_. It consists of an inflammation, involving the air cells and smallest air tubules of the lungs; in other words, it is an inflammation of the substance or tissues of the lungs. It is altogether a more serious affection than bronchitis, and in very small children exceedingly dangerous. The inflammation may affect either a small circumscribed portion of the lung, _lobular_ pneumonia, or it may compromise an entire lobe or all the lobes of the lung, and is then called _lobar_ pneumonia. Pneumonia is dangerous in proportion to the extent of lung tissue involved and the symptoms become correspondingly aggravated. The disease occurs extremely often in children, but it is altogether different from that which occurs in the adult. In children it is of a bronchial nature, that is, the ordinary bronchial catarrh has a tendency to extend to the very small bronchial tubes (capillary bronchitis), thence into the air cells of the lungs. In this variety of pneumonia the lungs do not become inflamed in their entirety, but here and there patches of lung tissue become the seat of lobular pneumonia. In the nursling, catarrhal pneumonia is an extremely frequent affection and I believe that it is principally due to the carelessness and promiscuous bathing of infants to which I have already referred. In foundling hospitals this disease destroys a great many children, and the chief cause has been attributed to their lying both night and day in a horizontal posture. It has been statistically proven that many more children suffer from the disease in winter than in summer, and further, that in those parts of the lung that are inflamed the bronchial tubes which lead to them are also found to be inflamed. This relation of catarrhal pneumonia to bronchitis may be accounted for by the play of a mechanical force and thus illustrates the relation of cause and effect. The secretion of bronchitis not being expectorated, gravitates into the region in which the inflamed bronchial tubes terminate, namely, the air cells of the lungs, and by irritating and blocking or filling the air cells, a catarrhal pneumonia is developed. The symptoms of pneumonia in children under two years of age are those of the catarrhal or lobular type; after they have passed through their first dentition they become subject to lobar pneumonia which differs in no particular from the disease which occurs in grown persons. Practice and experience make the discovery of catarrhal pneumonia possible in little children as soon as they are under observation for a little while. The most prominent sign is the rapidity of the respiration, which rises to sixty and eighty per minute instead of forty-four, the average normal respiration for the first year of infantile life.