The Merck Index is a one volume encyclopedia of chemicals, drugs and biologicals that contains more than 10,000 monographs. Each monograph is a concise description of a single substance or a small group of closely related compounds. The subjects covered include human and veterinary drugs, biologicals and natural products, agricultural chemicals, industrial and laboratory chemicals, and environmentally significant compounds. The information provided includes chemical, common and generic names, trademarks and their associated companies, Chemical Abstracts Service (CAS) Registry Numbers, molecular formulae and weights, physical and toxicity data, therapeutic and commercial uses, citations to the chemical, biomedical and patent literature, and chemical structures. In addition, there are Name, Formulae, CAS Registry Number and Therapeutic Category/Biological Activity indices. The collection of supplementary tables contains physical, chemical and biomedical data and listings of pharmaceutical company names, locations and experimental drug codes. The Organic Name Reactions section has been reintroduced with revised and updated content.