The respiratory system is one of the greatest channels through which communicable diseases are spread. In the classification of diseases which are spread by means of the respiratory system are to be found in such maladies as Influenza, Tuberculosis, Diphtheria, Pneumonia, Cerebral spinal meningitis, Measles, Scarlet fever, Smallpox, Whooping cough, Poliomyelitis, Mumps, Tonsillitis (septic sore throat), and others. To consider each of these conditions separately from an epidemiological standpoint, it would require more space than is permitted in a descriptive article of limited scope. For this reason, no mention is made of the epidemiology of those diseases which are thoroughly understood and clear cut from a public health point of view. The common, but less understood, conditions of common cold, sore throat (septic), tonsillitis, sinusitis, etcetera will be considered in more detail. Until within recent years the importance of the common cold and its associated maladies was considered rather trifling, but of late this attitude has changed considerably and it is now realized that a common cold, though it is a mild affair in most cases, is just as serious as one of the so-called serious communicable diseases. In view of the far-reaching consequences which may accompany and follow it, what is said regarding the common cold may also be said for tonsillitis, septic sore throat, and sinusitis. All are similar in many respects, though varying in others.