HYOSCYAMINE, one of the alkaloids (q.v.) of belladonna (q.v.). It is the chief source of atropine (q.v.), to which it stands in the relation of laevo-rotatory optical isomer, being converted to atropine by racemization (see STEREOCHEMISTRY). It crystallizes, like atropine, in colourless prisms, has a melting point 108.5° C, a specific rotation [ a } and the chemical formula C17H2303N. The sulphate forms needles from alcohol, has a melting point 206° C, and is the salt generally used in medicine.