LICHEN ISLANDICUS. 739 



moss as much as 70 per cent, of the so-called Lichenin or Lichen-starch, 

 a body which is perfectly devoid of structure. The decoction (1 : 20) 

 gelatinizes on cooling, and assumes a reddish or bluish tint by solution 

 of iodine. This property of lichenin is plainly seen, when the drug is 

 first exhausted by boiling spirit of wine containing some carbonate of 

 potassium ; and then boiled with 50 to 100 parts of water, and the decoc- 

 tion precipitated by means of alcohol. The lichenin thus obtained in a 

 purer state, must be deprived of alcohol by cautiously washing it with 

 water. Powdered iodine will now immediately impart to it while still 

 moist an intense blue. Its composition, C^'H^O^", agrees with that of 

 starch and cellulose ; and it must be regarded as a modification of the 

 latter, being likewise soluble in water and in amraoniacal solution of 

 copper. Lichenin is not a kind of mucilage, because it yields but 

 insignificant traces of mucic acid, if treated with concentrated nitric 

 acid ; and also because it contains no inorganic constituents.^ The verj^ 

 trifling proportion of mucic acid it furnishes may depend upon the 

 presence, in small amount, of an independent mucilaginous body. 



According to Th. Berg (1873), lichenin consists of what he continues 

 to call so, and another constituent, the latter only being coloured by 

 iodine, possessing (dextrogyre) rotatory power, and also being insoluble 

 in ammoniacal solution of copper. Berg's lichenin is not soluble in cold 

 water, but readily dissolves in hot water, and again separates on cooling. 

 The other constituent on the contrary is abundantly soluble in cold, 

 and very sparingly in hot water. The drug yielded to Berg 20 per cent, 

 of "true" lichenin and 10 per cent, of the other substance. 



The chlorophyll of the gonidia is not soluble in hydrochloric acid, 

 and hence is distinguished by Elnop and Schnedermann as Thallochlor ; 

 its quantity is extremely small. 



The bitter principle of Cetraria, called Cetraric Acid or Cetrarin, 

 (-ii8jji6Q8^ crystallizes in microscopic needles, is nearly insoluble in cold 

 water, and forms with alkalis, yellow, easily soluble, bitter salts. The 

 lichen also contains a little sugar, and about 1 per cent, of a peculiar 

 body, Licheno-stearic Acid, C^^H^O^ the crystals of which melt at 

 120° C. The Lichenic Acid found by Pfafi'in 1826 in Iceland moss, and 

 formerly regarded as a peculiar compound, has been proved identical 

 with fumaric acid. 



In common with many lichens, cetraria contains Oxalic Acid and is 

 said to yield also some tartaric acid. The ash, which amounts to 1-2 

 per cent., consists to the extent of two- fifths of silicic acid combined 

 chiefly with potash and lime. 



Collection and Commerce — Iceland moss is collected in many 

 districts where the plant abounds at least for local use, as in Sweden, 

 whence some is shipped to other countries. It is also gathered in 

 Switzerland, especially on the mountains of the Canton of Lucerne, and 

 in Spain.2 None is exported from Iceland. 



Uses — It is given in decoction as a mild tonic, combined with more 

 active medicines. It is very little employed in Iceland, and only in 

 seasons of scarcity, when it is sometimes ground and mixed with the 



^ The various mucilages and gums yield ^ Cat. of Spanish Productions,— Jjondon 



from 4 to 20 per cent, of ash, but lichenin Exhibition, 1851. 

 yields none. 



