The Uniqueness of Finger-prints (指纹的唯一性) Every human being has a unique arrangement of the skin on his fingers and this arrangement is unchangeable. Scientists and experts have proved the uniqueness of finger-prints and discovered that no exactly similar pattern is passed on from parents to children, though nobody knows why this is the case. The ridge structure on a person’s fingers does not change with growth and is not affected be suce injuries. Burns, cuts and other damage to the outer part of the skin will be replaced in time by new one, which bears a reproduction of the original pattern. It is only when the inner skin is injured that the arrangement will be destroyed. Some criminals make use of this fact to remove their own finger-prints but this is a erous and rare step to take. Finger-prints can be made very easily with printer’s ink. They can be recorded easily. With special methods, identification can be achieved successfully within a short time. Because of the simplicity and economy of this system, finger-prints have often been used as a method of solving criminal case. A suspected man may deny a charge but this may be in vain. His finger-prints can prove who he is even if his appearance has been changed by age or accident. When a suspect leaves finger-prints behind at the scene of a crime, they are difficult to detect with the naked eye. Special techniques are used to "develop" them. Some of the marks found are incomplete but identification is possible if a print of a quarter of an inch square can be obtained.

finger-prints have often been used as a method of solving criminal case because it ______.