Pigmented substances introduced may lodge in the tissues and even permanently colour them. Salts of silver, when long administered, or when taken in excess in one dose, may cause a bluish staining of the skin - Argyria. The oxide of silver is deposited also in the tissues of internal organs.

The Dust of the air which is inhaled, passes to some extent into the substance of the lungs, and gives a dark colour to them. (See under Lung Diseases.) Workers whose trades expose them to variously coloured dust, present similar pigmentations of the lungs. Tattooing is an operation by which granular pigments are introduced, and lodge in or under the skin and in the lymphatic glands.