kidney, artificial, mechanical device capable of assuming the functions ordinarily performed by the kidneys. In treating cases of kidney failure a tube is inserted into an artery in the patient's arm and blood is channeled through semipermeable tubes immersed in a bath containing all the normal blood chemicals except urea and other metabolic waste products. Since the concentration of harmful metabolic wastes are higher in the blood than in the bath, they pass through the walls of the tubes into the bath and purified blood is returned to the body. This process of blood purification, called hemodialysis (see dialysis), is continuous or intermittent, depending on the residual kidney function in the patient. Kidney transplants usually make hemodialysis unnecessary.