Artificial organ almost always preceded by extensive experiments with animals. Initial testing in humans is frequently limited to those either already facing death or who have exhausted every other treatment possibility. Artificial arms and legs, or prosthetics, are intended to restore a degree of normal function to amputees. Mechanical devices that allow amputees to walk again or continue to use two hands have probably been in use since ancient times, the most notable one being the simple peg leg. Since then, the development of artificial limbs has progressed rapidly. New plastics and other materials, such as carbon fiber have allowed artificial limbs
Environmental medicine studies viruses, bacteria and fungi are not within the scope of environmental medicine, if the spread of infection is directly from human to human. However, infections that are water-borne (e.g. cholera and gastroenteritis caused by norovirus or campylobacteria), or food-borne, are typical concerns of environmental medicine. Its role is preventive as far as possible. Much of epidemiology, which studies patterns of disease and injury, is not within the scope of environmental medicine, but e.g. air pollution epidemiology is a highly active branch of environmental health and environmental medicine. In addition, any disease with a large genetic component usually falls outside