The Source of Infectious Material.—­t has been learned that for most diseases the infectious material comes from individuals suffering with the disease, and that except in a few cases, like malaria, we must always look to individuals suffering from disease for all sources of contagion.  It is found that pathogenic bacteria are in all these cases eliminated from the patient in some way, either from the alimentary canal or from skin secretions or otherwise, and that any nurse with common sense can have no difficulty in determining in what way the infectious material is eliminated from her patients.  When this fact is known and taken into consideration it is a comparatively easy matter to devise valuable precautions against distribution of such material.  It is thus of no small importance to remember that the simple presence of bacteria in food or drink is of no significance unless these bacteria have come from some source of disease infection.

The Method of Distribution.—­The bacteria must next get from the original source of the disease to the new susceptible individual.  Bacteria have no independent powers of distribution unless they be immersed in liquids, and therefore their passage from individual to individual must be a passive one.  They are readily transferred, however, by a number of different means, and the study of these means is aiding much in checking contagion Study along this line has shown that the means by which bacteria are carried are several.  First we may notice food as a distributor.  Food may become contaminated by infectious material in many ways; for example, by contact with sewage, or with polluted water, or even with eating utensils which have been used by patients.  Water is also likely to be contaminated with infectious material, and is a fertile source for distributing typhoid and cholera.  Milk may become contaminated in a variety of ways, and be a source of distributing the bacteria which produce typhoid fever, tuberculosis, diphtheria, scarlet fever, and a few other less common diseases.  Again, infected clothing, bedding, or eating utensils may be taken from a patient and be used by another individual without proper cleansing.  Direct contact, or contact with infected animals, furnishes another method.  Insects sometimes carry the bacteria from person to person, and in some diseases (tuberculosis, and perhaps scarlet fever and smallpox) we must look to the air as a distributor of the infectious material.  Knowledge of these facts is helping to account for multitudes of mysterious cases of infection, especially when we combine them with the known sources of contagious matter.