foreign objects that penetrate the body from without. They cause changes in the body that vary with their size, shape, physical and chemical properties, presence of bacterial flora, and mechanism of their entry and location. Chemically active foreign bodies (for example, lead of indelible pencils) may produce an inflammatory reaction in the surrounding tissues and even cause necrosis. In blind fragmentation and bullet wounds, pieces of clothing, dirt, and so forth may lodge in the tissues along with the metal of the projectile. Bacterially contaminated foreign bodies cause suppuration. Foreign bodies may cause pain by pressing against nerves and result in vascular hemorrhage or perforation, but they can also remain in the body for many years without complications. In daily life, foreign bodies occur most frequently in children who swallow, inhale, and stuff into the nose and ear all kinds of objects. Adults accidentally swallow meat and fish bones and sometimes (while asleep or in a faint) their dentures.

Foreign bodies are removed from the respiratory tract of the pharynx and esophagus mainly with an endoscope. In the stomach and intestine, foreign bodies, even those with sharp edges, often move along harmlessly during peristaltic contractions and leave the body naturally. A type of food that coats (gruel, puree, fruit jelly, milk) is prescribed in such cases, and the movement of the foreign body is followed by X-rays. Foreign bodies in the eyes are removed with a tampon or magnet. Attempts by the individual to extract foreign objects by himself may result in rupture of the eardrum, injury to the cornea, and so forth.

Foreign bodies inserted into the body for therapeutic purposes for a certain period of time (pin to join together bone fragments after a fracture, cardiac pacemaker in heart block) or permanently (vascular prosthesis, cardiac valve) are in a class by themselves. Such foreign bodies should not irritate live tissues. The surfaces of prostheses coming in contact with blood should be absolutely smooth so as not to cause the formation of thrombi in the blood.