Cetraria islandica. Iceland Moss.
Nat. Ord. — Lichenaceae. Sex. Syst. — Cryptogamia Lichenes.
Description. — Iceland Moss is a perennial, foliaceous plant, from two to four inches high ; thallus erect, tufted, olive-brown, paler on one side, laciniated, channeled, and dentato-ciliate, the fertile laciniae very broad. Shields brown, appressed, flat, with an elevated border.
History. — This lichen is a native of Britain and the northern countries of Europe, particularly Iceland. It is of various colors, being grayish-white, brown, and red in different parts ; has a bitter, mucilaginous, somewhat astringent taste ; is inodorous, absorbs more than its weight of water when steeped, rendering the water bitter if warmed, is converted into a mucilaginous pulp by long chewing, and when boiled in water the decoction becomes a firm jelly on cooling. The bitter principle, winch may be removed by weak alkaline solutions, is called Cetrarin, and is used in Italy instead of Cinchona. It may be obtained by boiling the coarsely-powdered moss for half an hour in four times its weight of alcohol of 0.883. When tepid, the solution is to be filtered, and treated with diluted muriatic acid, in the proportion of three drachms to every pound of moss employed. Water, to the amount of four times the volume of the liquid, is then to be added, and the mixture left for a night in a closed matrass. The deposit which forms, is collected on a filter, allowed to drain as much as possible, and submitted to the press. To purify it, break the mass into small pieces, and while still moist, wash it with alcohol or ether, then treat it with two hundred times its weight of boiling alcohol, which dissolves only the cetrarin; as the liquid cools, this is, for the greater part deposited, and the remainder may be obtained by evaporation. One pound of moss will thus yield about 133 grains of cetrarin. It is white, uncrystalline, light, permanent in the air, inodorous, and very bitter, especially in tincture. It is soluble in absolute alcohol, ether, and slightly so in water; alkalies form permanent compounds with it, from which it may be separated by acids with its original properties unchanged. Acids do not unite with it, and its solutions are neutral to test-paper. Concentrated hydrochloric acid converts it into a bright-blue coloring matter. It precipitates the salts of iron, copper, lead, and silver, and has been used in two-grain doses, repeated every two hours, with much success in intermittents. It is supposed to consist of cetraric acid, lichstearic acid, and thallocor.
The most important part of Iceland moss, is its nutritive principle, to which the name of Lichenin has been given. It may be obtained by macerating the chopped lichen for twenty-four hours, in eighteen parts of water, containing a 250th of its weight of carbonate of potassa — strain off the bitter solution without pressure;, and remove the rest of it from the residuum by maceration with cold water, and simple straining. Boil the residuum in nine parts of water down to six, strain the decoction, and squeeze what is left in the cloth, and then allow the strained liquor to cool. A firm jelly is formed, which cracks and throws out much of the water, and then dries into a hard, black, glassy-like substance. The black coloring matter may be removed by boiling again, straining, cooling, and drying; upon which the lichenin is obtained in thin, transparent, and tough plates of a yellowish color. Cold water renders it gelatinous, boiling water dissolves it, forming a jelly on cooling ; alcohol and ether do not affect it. Iodine renders its watery solution blue, and it is converted into sugar by sulphuric acid, and into oxalic acid by nitric acid. It consists of carbon, oxygen, and hydrogen, and in some respects resembles amidin.
Properties and Uses. — Demulcent, tonic, and nutritious. Used as a demulcent in chronic catarrhs, chronic dysentery, and diarrhea, and as a tonic in dyspepsia, convalescence, and exhausting diseases. Boiled with milk it forms an excellent nutritive and tonic in phthisis, and general debility. Its tonic virtues depend upon its cetrarin, which, if removed, renders the lichen merely nutritious.
Off. Prep. — Decoctum Cetrariae.