DISEASES OF THE RESPIRATORY SYSTEM The diseases of the organs of respiration in the infant, may be considered the most frequent and important affections, and are only surpassed in importance, during the nursing period, by the gastro-intes tinal disorders. As early as the second half year of life, the disorders of the respiratory system increase very rapidly; indeed, they occupy the first place in regard to frequency and mortality until the third and fourth year, occurring either primarily or secondarily to certain infectious diseases (whooping-cough, measles, influenza).
Krieger has shown in his splendid etiological studies (Strassburg, 1877) that after the beginning of extra-uterine life, the tendency to ca tarrhal inflammations and to other diseases of the organs of respiration, develops only gradually, passing downwards from the nose to the lungs. A coryza may occur in the newborn after the first week; but only later, at about the middle of the second month, the larger air-passages show a tendency to catarrhal inflammations, and as a general rule, still later, the finer bronchi and the lungs. The infant is born with healthy
mucous membranes, and the noxious principles entering the body through the respired air require a certain length of time in order to render the tissues susceptible to disease. Naturally, the periphery of the mucous membrane (the nose) is the first to be involved, since it is primarily ex posed. The bronchi and lungs remain uninvolved, and are capable of resistance for ft longer period, because they are more distantly situated from the outer world. The air passing through the bronchi is rendered harmless, or at least less harmful, by the known means of protection of the more peripherally situated mucous membranes (ciliated epithelium, bactericidal properties).
Moreover, the deeper seated a morbid process is, the later will the disposition to disease be established. For this reason, therefore, inflam matory conditions of the bronchi, rather than those of the lung tissue, occur during the early years of life.