4. Agar or Agar-agar, U.S.P. IX.
4. AGAR OR AGAR-AGAR U.S.P. IX.—The dried mucilaginous substance extracted from Gracilaria (Sphaercocus) lichenoides.
Gracilaria and other marine Algae, growing along the eastern coast of Asia, particularly several species of Gelidium or Gloiopeltis (class Rhodophyceae). Mostly in bundles 4 to 6 dm. in length, thin translucent, membranous, agglutinated pieces from 4 to 8 mm. in width; externally yellowish-white, shiny; tough when damp, brittle when dry; odor, slight; taste, mucilaginous. Tests show it to be insoluble in cold but slowly soluble in hot water. No gelatin or no starch, etc.
TEST.—Practically the same as that for chondrus. Ash, not more than 5 per cent. Average dose, 10 Gm. (2 ½ dr.).
ACTION AND USES.—Agar-agar is practically never used in medicine. It possesses demulcent and emulsifying properties in common with other species of Algae. It is principally used at present in bacteriological laboratories as a culture medium for micro-organisms.
Agar-agar in the dry state passes through the stomach undigested and on reaching the bowels takes up water and swells considerably, thereby increasing the volume of the evacuations; it is therefore considered a laxative.