An eleven-amino acid neurotransmitter that appears in both the central and peripheral nervous systems. It is involved in transmission of pain, causes rapid contractions of the gastrointestinal smooth muscle, and modulates inflammatory and immune responses.
A chemical material, e.g. a drug.
Matter or material. A generic word used for simplicity, as in “dangerous substance,” to be inclusive of all chemicals, drugs, biological agents, and other materials which are dangerous.
Material of which any organ or tissue is composed; matter.
A solitary form of substance characterized by an unambiguous and unwavering constitution.