Colorless, endogenous or exogenous pigment precursors that may be transformed by biological mechanisms into colored compounds; used in biochemical assays and in diagnosis as indicators, especially in the form of enzyme substrates. Synonym: chromogens (not to be confused with pigment-synthesizing bacteria also called chromogens).

The location of the atoms, groups or ions relative to one another in a molecule, as well as the number, type and location of covalent bonds.

Inorganic or organic compounds that contain sulfur as an integral part of the molecule.

Works containing information articles on subjects in every field of knowledge, usually arranged in alphabetical order, or a similar work limited to a special field or subject. (From The ALA Glossary of Library and Information Science, 1983)

'Printing' in a medical context refers to the temporary or permanent transfer of ink from a substrate to the skin, often used for identification purposes, monitoring medical conditions, or as a form of temporary decoration.

The visually perceived property of objects created by absorption or reflection of specific wavelengths of light.

An acid dye used in testing for hydrochloric acid in gastric contents. It is also used histologically to test for AMYLOIDOSIS.

Method of making images on a sensitized surface by exposure to light or other radiant energy.

Silver. An element with the atomic symbol Ag, atomic number 47, and atomic weight 107.87. It is a soft metal that is used medically in surgical instruments, dental prostheses, and alloys. Long-continued use of silver salts can lead to a form of poisoning known as ARGYRIA.

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