AGAR-AGAR 217 



viz. G. elegans, Kutz., G. Amansii, Kutz. (N.O. Rhodophycece) . The 

 name is also applied to various algae, e.g. Gracilaria lichenoides, Greville 

 (Ceylon agar-agar), Eucheuma spinosum, Agardh (Macassar agar- 

 agar), &c. 



Commercial agar-agar is made by boiling the carefully washed algse 

 with water, straining with pressure, cooling, cutting the jelly into 

 strips and slowly drying. 



Description. Japanese agar-agar occurs in transparent strips 

 about 6 dm. long and about as thick as a straw, or in yellowish white 

 pieces about 3 dm. long, 2-5 to 25 mm. thick and more than 25 mm. 

 wide. The decoction (1 to 200) solidifies on cooling to a jelly which 

 melts at a much higher temperature than a similar jelly prepared 

 from gelatin. In cold water it swells but does not dissolve. 



Constituents. Agar-agar consists chiefly of the carbohydrate gelose 

 which is converted by boiling with dilute sulphuric acid into galactose. 

 It always contains skeletons of diatoms (e.g. Arachnoidiscus ornatus) 

 by which its presence in preserves can be readily detected. 



Uses. Agar-agar is largely used for the preparation of bacterio- 

 logical culture media, the high melting-point (40) of the jelly render- 

 ing it for this purpose particularly suitable. It passes through the 

 intestinal canal almost unchanged, but absorbs water during its 

 passage and promotes peristalsis. 



CETRARIA 



(Iceland Moss) 



Source, &c. Iceland moss, Cetraria islandica, Acharius (Class, 

 Fungi ; Subclass, Ascomycetes ; Order, Discomycetes) , is a foliaceous 

 lichen indigenous to Great Britain and widely distributed over the 

 northern hemisphere. It is collected chiefly in Sweden and Central 

 Europe, growing usually amidst moss and grass on the lower mountain 

 slopes. 



Description. The lichen consists of a very thin, erect, leafy thallus, 

 branching fanlike into curled or flattened papery lobes about 6 mm. 

 broad, fringed with minute projections each of which terminates 

 in a spermagonium containing numerous spermatia capable of 

 reproducing the plant. It is remarkably harsh and springy to the 

 touch, tough when slightly moist, but brittle when quite dry. The 

 upper surface is usually of a brownish or greenish brown colour ; 

 the under surface greyish and marked with numerous small, white, 

 depressed spots. The apothecia are circular, of a dark reddish 

 brown colour, and about 5 mm. in diameter ; they are not 

 often to be found on the plant. The drug is almost odourless, and 



