690 BOTANY AND PHARMACOGNOSY. 



which is widely distributed over the northern part of both conti- 

 nents (p. 40). The chief commercial supplies are obtained from 

 Scandinavia, Germany, Switzerland and parts of Austria. 



Description. — Consisting of a number of somewhat dichoto- 

 mously branching, more or less curled, papery, fringed segments, 

 5 to 10 cm. long and about 5 mm. wide ; upper surface greenish- 

 brown, with occasional dark reddish-brown cupular apothecia; 

 under surface grayish, with numerous small, whitish, depressed 

 spots ; tough when damp, but brittle when dry ; odor slight ; taste 

 mucilaginous and bitter. 



Constituents. — The principal constituents are lichenin and 

 isolichenin (about 70 per cent.), the former of which appears to 

 be intermediate between starch and cellulose, and is soluble in 

 hot water, the solution becoming gelatinous on cooling, but not 

 colored blue with iodine; isolichenin (dextrolichenin) somewhat 

 resembles soluble starch, being soluble in cold water and giving a 

 blue reaction with iodine. The drug also contains 2 to 3 per cent, 

 of a bitter crystalline principle, cetrarin, which is colored blue with 

 concentrated hydrochloric acid and yields on hydrolysis cetraric 

 acid, which is also intensely bitter ; 1 per cent, of a tasteless, crys- 

 talline principle, lichenostearic acid; several organic acids, as 

 oxalic, tartaric and fumaric (lichenic) ; about 15 per cent, of 

 cellulose; about 3.6 per cent, of an uncrystallizable sugar; 3.7 

 per cent, of gum; a principle resembling chlorophyll thallochlor, 

 which is unaffected by hydrochloric acid; and yields less than 

 2 per cent, of ash. 



The bitter principle in Cetraria may be removed by treating 

 the drug with a i per cent, solution of potassium carbonate at 

 about 60° C. for several hours. 



Iceland moss jelly (Gelatina lichenis islandica) is official in the 

 German Pharmacopoeia, and is prepared by making a decoction 

 of 3 parts of washed cetraria and 100 parts of water, adding 

 three parts of sugar and evaporating the whole to 10 parts. Dried, 

 saccharated Iceland moss, which is official in the French Codex, is 

 prepared somewhat similarly to the Iceland moss jelly, but the 

 product is evaporated to dryness and then powdered. 



Allied Plants. — Usnea barbata and Cornicularia aculeata 

 contain a principle resembling lichenin, which on hydrolysis yields 



