The environment in which people live has an enormous influence on health, the extent to which the health situation in a country can be improved by modifications to its environment is difficult to quantify. Providing adequate quantities of food and water of acceptable quality and breaking the oral-fecal chain are essential to reducing gastrointestinal diseases. These had already declined significantly in most of Europe and North America before the introduction of certain therapeutic drugs and oral rehydration therapy. Similarly, while immunization and the use of modern drugs have contributed...