a term applied to certain diseases which appear at intervals in various parts of the world and affect a large number of people. All of these diseases have their source in minute bacteria, which are born and developed in decaying animal and vegetable matter or in stagnant pools. The best preventive of these diseases is complete drainage and perfect sanitation. The paving of streets, building of sewers and the filtration of drinking water all are certain preventive measures. The development of serum therapy has already made possible the prevention of many of these diseases, such as smallpox and diphtheria, and it promises to find preventives for most, if not all, of the others.