ELEMENTS OE MATERIA MEDICA.

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lichenates of potash and lime mixed with phosphate of lime, l - 9 ; amylaceousfibrin, 36 ’2.

The starchy matter (lichenin,feculoid substance of lichens) is somewhat different fromordinary starch. No particles analogous in their physical properties to other feculas canbe observed. Water extracts a substance like amidin (the soluble matter of fecula).But as no boiling, however long continued, deprives the insoluble texture of Icelandmoss of the property of being tinged blue by iodine, Raspail (Chim. Organ, i. 540) infersthat the amylin (the insoluble or membranous portion of fecula) remains enveloped inthe texture in which it was formed; thus constituting, I presume, the amylaceous fibrinof Berzelius . Lichenin is composed of C'° H u O 10 .

The bitter principle (cetrarin) is white, intensely bitter, soluble in alcohol (especiallyat a boiling temperature), ether, less so in water, volatile oil, and creosote. It is colouredblue by hydrochloric acid when aided by heat, combines with alkalies, and forms a redprecipitate with the salts of iron, and a greenish one with those of copper (Herberger,Journ. de Pharm. xxiii. 505).

Lichenic acid is composed of C 4 H 2 O 4 . It forms a reddish precipitate with the per-salts of iron.

Chemical Characteristics. —Iceland moss swells up in cold water,to which it communicates a brownish tint. Boiled in water it yields aliquid which, when sufficiently concentrated, gelatinizes on cooling.The decoction, when cold, forms with iodine a blue compound ( iodide ofamidin ) ; with the sesquichloride of iron, a dingy purplish red ( cetrarateand lichenate of iron) ; with diacetate of lead, a copious whitish pre-cipitate ( amidate of lead) ; w r ith sulphate of copper and caustic potash,a green precipitate ( cetrarate of copper).

Physiological Effects, (a.) On animals. —In Camiola,pigs, horses,and oxen, are fattened by it (Murray, App. Med. v. 506).

( b .) On man. —It is a mucilaginous or demulcent tonic, without anytrace of astringency. If the bitter matter ( cetrarin) and extractive beremoved, it is nutritive, emollient, and demulcent, like ordinary starch,over which it has no advantage. Captain Sir John Franklin and hiscompanions tried it as an article of food, when suffering great privationsin America , but its bitterness rendered it hardly eatable ( Narrative of aJourney to the Shores of the Polar Sea, p. 414. 1823).

Uses. —Iceland moss is well adapted to those cases requiring a nutri-tious and easily-digested aliment and a mild tonic, not liable to disorderthe stomach. It has been principally recommended in chronic affectionsof the pulmonary and digestive organs, particularly phthisis, chroniccatarrh, dyspepsia, chronic diarrhoea, and dysentery; but its efficacy hasbeen much exaggerated.

Administration. —It is best exhibited in the form of decoction.When employed as an alimentary substance merely, the bitter mattershould be extracted before ebullition. This is effected by digesting thelichen in a cold weak alkaline solution (composed of water 300 parts,and carbonate of potash 1 part), and afterwards w-ashing it with coldwater. It is then to be boiled in water or milk. When the decoction issufficiently concentrated, it gelatinizes on cooling. It may be flavouredwith sugar, lemon peel, white w ine, or aromatics, and then forms a veryagreeable kind of diet.

Dkcoctum Cetrarim, Ph . Lond.—Iceland moss, 5v.; water, Ojss.;boil dow r n to a pint, and strain. The dose is from f5j. to f3iv. every f° liror six hours. The Dec. Lichenis Islandici, Ph . Edinb., is prepared byboiling oj. of the moss with Ibij. of water to 16 ounces. The Dublincollege orders hall an ounce of the moss to be digested for two hours in