A form of gelose extracted from seaweeds of several species. Agar, or agar-agar, as it is commonly called, is not digested, but absorbs large quantities of water in the stomach and intestines, forming a jelly which increases the bulk of the feces.

Agar is employed in the treatment of constipation, administered in substance, eaten with a cereal or baked in crackers or biscuits. It is official in the U. S. P., IX, and the dose is given as 2 drachms.