Endemic diseases are those which are constantly present in a community because of certain unfavorable conditions, such as malaria in swampy regions, rheumatism from bad climatic conditions, and diseases resulting from unhealthy employments. Miasmic diseases are those due to conditions of the soil, and comprise the various forms of intermittent fevers, agues and the like. Infectious diseases, on the other hand, belong to the people, and not to the place. They are communicated from one person to another through the air, or by means of infected articles of clothing, etc., and they attack the strong and healthy, no less than the weak. Among such are smallpox, scarlet fever, measles, etc. Various branches of infectious diseases are recognized in addition, as combining some of the characteristics of the classes already named. For instance, erysipelas and other blood poisons are generated with the body of the individual who, so to speak, infects himself and may then infect others. Typhoid, cholera and yellow fever are miasmic diseases, but they are also capable of being carried by human intercourse, infected clothes, polluted water, etc., within certain limits of space and time. Hydrophobia, glanders and such diseases are communicated only by actual contact of body. Rickets and scurvy are preventable, though not communicable diseases, being direct results of mal-nutrition or imperfect nourishment, and consequently are diseases of diet. Bacteria are those minute organisms which under various names are the active causes not only of diseases but of all putrefaction, fermentation and like changes in dead organic matter. Like all living things they may be killed, and on this is based the whole theory of disinfection. Some are more hardy than others, under conditions which are frequently supposed to be unfavorable to them. Merely to destroy an unpleasant odor or to admit fresh air into a room does not mean to disinfect, and it is necessary to understand this clearly in the effort to purify rooms in the event of infection. Contagion is communicated sometimes with the utmost ease, if the new victim be in a receptive condition, and in the presence of any disease, even the most simple, it is well to take every precaution. The mucous surfaces are peculiarly ready to absorb infection of many kinds. Measles is easily absorbed from pocket handkerchiefs, as are also scarlet fever, whooping-cough and other diseases. By inhalation through the nostrils or mouth, scarlet fever, measles, whooping-cough, mumps, diphtheria, dysentery, cholera and even pneumonia and meningitis may be communicated. By eating or drinking something which contains the germs of cholera, typhoid, malaria, tuberculosis or consumption, diphtheria and scarlet fever, these diseases are communicated. HOW TO PREVENT CONTAGION