History.—The medicinal properties of this plant (usually termed Lichen islandicus) were probably first known to the natives of Iceland. According to Borrichius, the Danish apothecaries were acquainted with them in 1673. In 1683, Hiärne spoke favourably of its effects in haemoptysis and phthisis.
Botany. Gen. Char.—Thallus foliaceous, cartilagino-membranaceous, ascending and spreading, lobed and laciniated, on each side smooth and naked. Apothecia orbicular, obliquely adnate with the margin of the thallus, the lower portion being free (not united with the thallus); the disk coloured, plano-concave, with a border formed of the thallus and inflexed (Hooker).
Sp. Char.—Thallus erect, tufted, olive brown, paler on one side, laciniated, channelled, and dentatociliate, the fertile lacinia very broad. Apothecia brown, appressed, flat, with an elevated border (Hooker).
Hab.—Dry mountainous districts of the new and old continents. Although met with in considerable abundance in Scotland, it is never gathered there as an article of commerce.
The word cetraria is derived from cetra or caetra (καιτρεα, Hesych), an ancient shield made of leather, which the apothecia are supposed to resemble.
Collection.—The lichen should be collected on dry and clear days, carefully deprived of all foreign matter by hand-picking, and dried in the sun.
Physical Properties.—The Iceland moss of commerce (muscus islandicus; lichen islandicus) is in general brownish or grayish white; the upper surface darker, towards the base sometimes marked with blood-red spots; the under surface paler, whitish, with white spots which have a chalky or mealy appearance, are lodged in little depressions of the thallus, and when submitted to microscopic examination appear warty, pearl-white masses. Apothecia are rather rare on the commercial lichen. When quite dry, the lichen is crisp, cartilaginous, and coriaceous. It is almost odourless, and has a bitter mucilaginous taste. Its powder (farina) is whitish gray.
Commerce.—It is imported in barrels and bags from Hamburgh and Gottenburgh, and is said to be the produce of Norway and Iceland. In 1836, 20,599 lbs. paid duty; in 1837, 12,845 lbs.; in 1838, 6179 lbs.; in 1839, 15,933 lbs.; and in 1840, 6462 lbs.
Composition.—It was analyzed by Berzelius [Ann. de Chim. xc. 277.] in 1808, who obtained the following products from 100 parts:—green wax, 1.6; yellow extractive matter, 7.0; bitter matter, 3.0; uncrystallizable sugar, 3.6; gum, 3.7; starch, 44.6; starchy skeleton, 36.2; gallic acid, trace; bitartrate of potash, tartrate of lime, and a little phosphate of lime, 1.9 (=101.6). In 1844-5 it was examined by Messrs. Schnedermann and Knop [Annal. der Chim. u. Pharm. Bd. iv. S. 144, 1845; Pharm. Journ. vol. v. p. 427, 1846.].
The following figures represent the microscopic appearances of sections of the lichens.
Sections of Cetraria Islandica (highly magnified).
a. External or cortical layer, which does not become blue by the addition of the tincture of iodine.
b. Subcortical layer (stratum gonimicum, Wallroth; stratum faculare, Wahlenberg), which becomes blue on the addition of tincture of iodine.
c. Medullary layer, composed of felted filaments or tubes (tela contexta, Schleiden), and intermixed nucleated cells (annuli, Link).
1. Amylaceous Matter.—Cetraria islandica contains at least two kinds of amylaceous matter, namely, one which is coloured blue by iodine (lichen-starch), and one which does not become blue with this agent (inuline).
Link [Icones selectae Anatomico-Botanicae, Fascic. iii. Berlin, 1841.] states that the amylaceous matter of Cetraria does not occur in a globular form. If by amylaceous matter is to be understood starch grains, which are rendered blue by iodine, my observations confirm his statement. Payen [L'Institut de 1837, p. 145.], however, says he has seen the starch of Iceland moss in the form of little balls; but he has probably mistaken the cells for starch grains. When a thin section of the thallus has been soaked in cold water and then placed under the microscope, a general blue tint is communicated to the subcortical layer (see Figs. 167 and 168), on the addition of tincture of iodine: but none of the cells or granules become blue. A starchy nongranular matter, rendered blue by iodine, appears to reside in the intercellular tissue of the sucortical layer. My friend Mr. Henry Deane has traced this amylaceous matter to the surface of the apothecia, which appears to be deficient in the cortical non amylaceous layer. Moreover, iodine colours sections of the apothecia in stripes; rendering blue the starchy matter between the thecae and elongated cells (see Fig. 169).
I have sometimes seen the nucleated cells of the medullary layer (see Fig. 168) assume an amber colour when treated with iodine. Is this owing to the presence of inuline?
α. Lichen-starch. This becomes blue on the addition of iodine. According to Schnedermann nnd Knopp, hydrochloric acid converts it into a transparent jelly. Its formula, according to Mulder, is C12H10O10.
Even after very prolonged boiling in water the tissue of Iceland moss still retains the property of being tinged blue by iodine: hence it has been called amylaceous tissue, starchy skeleton, &c. Mulder says, that when boiled sufficiently and acted on by solvents, the final residue of it is nothing but cellulose: it is improper, therefore, to call it amylaceous tissue.
β. Inuline. This, according to Payen and others, is a constituent of Iceland moss. It is tinged yellow by iodine. When insoluble in cold water its formula is probably C12H10O10.
Mulder is of opinion that the chief part of lichen-starch must be composed of a starch which like inuline is turned yellow by iodine, and like common starch can be precipitated by basic acetate of lead.
2. Cetraric Acid; Cetrarin; bitter principle of Iceland moss.—This resides in the cortical portion of the thallus. It exists there for the most part in the state of free cetraric acid, and not as a cetrarate. In the pure state the acid occurs in the form of shining minute acicular crystals. It is intensely bitter, not volatile, and is infusible without decomposition. It is almost insoluble in water, which, however, acquires a bitter taste when boiled with the acid. It is soluble in boiling alcohol, but crystallizes in great part on cooling. It is slightly soluble in ether, and is quite insoluble in the fixed and volatile oils. Its formula is C34H16O15. It is dissolved both by the caustic and carbonated alkalies, and is precipitated from its solution by acids. Cetrarate of ammonia (2NH3, C34H16O15) is a beautiful yellow salt, having a faint ammoniacal odour, anil being soluble in water. By exposure to the air it gradually becomes brown. Schnedermann explains the production of the brown colour of Iceland moss by supposing that the cetraric acid of the thallus absorbs atmospheric ammonia, and the cetrarate of ammonia thus formed becomes brown by exposure to the air. The alkaline cetrarates yield a red colour (cetrarate of iron) with the salts of the peroxide of iron. Now as the ashes of Iceland moss contain iron, Schnedermann thinks it not improbable that the red spots which are sometimes found at the base of the lichen may be due to the presence of cetrarate of iron, produced by the action of cetrarate of ammonia (formed as above explained) on the ferruginous constituent. Cetrarate of lead (2PbO,C34H16O15) forms a yellow flocculent precipitate.
3. Lichestearic Acid (so called from λειχην, lichen; and στεαρ, fat). When pure it is perfectly white, and consists of pearly crystalline plates. It is odourless, but has an acrid taste. It is soluble in alcohol, ether, and the volatile and fatty oils, but is insoluble in water. At 248° F. it melts, and on cooling congeals into a crystalline mass. It cannot be volatilized without decomposition. Its formula is C29H25O6. It is dissolved by alkalies, and is precipitated from its alkaline solution by acids. Lichestearale of potash is a white indistinctly crystalline powder: Lichestearate of silver (AgO,C29H24O5) is grayish white: Lichestearate of lead (PbO,C24H24O5) is white: Lichestearate of baryta is grayish white: Lichestearate of ammonia is crystallizable.
4. Fumaric Acid; Lichenic acid.—This acid was discovered in Iceland moss by Pfaff.
5. A neutral substance, called provisionally "the body C," is mentioned by Schnedermann as being contained in tolerable quantity in the lichen. It is white, tasteless, insoluble in water, ether, oils, alkalies, and acids, and difficultly soluble in hot spirit.
Chlorothalle; Thallochlor.—This is the green colouring matter. It is soluble in ether, alcohol, and petroleum. It has the properties of a weak acid, and is distinguished from chlorophylle by being little or not at all soluble in hydrochloric acid.
Chemical Characteristics.—Iceland moss swells up in cold water, to which it communicates some portion of bitterness, and a very little mucilage. If to the moistened thallus some tincture of iodine be added, the tissues become intensely blackish blue; but the white chalky or mealy-looking spots, before mentioned, are unaltered by iodine, and appear more brilliantly white, in consequence of the black ground on which they are placed.
By prolonged boiling in water, the lichen yields a mucilaginous decoction, which, when sufficiently concentrated, gelatinizes on cooling. A solution of iodine communicates a blue colour (iodide of starch) to the cold decoction.
When the decoction has been imperfectly prepared in consequence of being weak, and insufficiently boiled, it yields a dingy green colour with iodine. The green colour depends on the mixture of two coloured substances: one yellow, the other blue. "If," says Mulder, "a diluted decoction of Iceland moss, after being coloured with iodine, is allowed to settle for a while, the layer at the bottom is yellow, and that immediately above is blue."
The decoction yields, with the basic acetate of lead, a copious whitish precipitate (amylate of lead); and with a mixture of sulphate of copper and potash, a green precipitate (cetrarate of copper) [Herberger, Journ. de Pharm. xxii.].
The sesquisalts of iron communicate a red colour (cetrarate of iron), both to the decoction and to an alcoholic tincture of Iceland moss (prepared by digesting 3ij of the lichen in f℥vj of rectified spirit).
In strong hydrochloric acid the thallus swells up, owing to the gelatinization of the starch contained in the intercellular spaces.
Physiological Effects. α. On animals.—In Carniola, pigs, horses, and oxen are fattened by it [Murray, App. Med. v. 506.].
β. On Man.—It is a mucilaginous or demulcent tonic, without any trace of astringency. If the bitter matter (cetraric acid) and extractive be removed, it is nutritive, emollient, and demulcent, like ordinary starch, over which it has no advantage. Captain Sir John Franklin and his companions tried it as an article of food, when suffering great privations in America, but its bitterness rendered it hardly eatable [Narrative of a Journey to the Shores of the Polar Sea, p. 414, 1823.].
Uses.—Iceland moss is well adapted to those cases requiring a nutritious and easily-digested aliment, and a mild tonic not liable to disorder the stomach. It has been principally recommended in chronic affections of the pulmonary and digestive organs, particularly phthisis, chronic catarrh, dyspepsia, chronic diarrhoea, and dysentery; but its efficacy has been much exaggerated.
Administration.—It is best exhibited in the form of decoction. When employed as an alimentary substance merely, the bitter matter should be extracted before ebullition. This is effected by digesting the lichen in a cold weak alkaline solution (composed of water 300 parts, and carbonate of potash 1 part), and afterwards washing it with cold water [Dr. Davidson, in a paper On the Removal of the bitter taste and lichenous odour of Iceland Moss (Jameson's Edinb. New. Phil. Journ. vol. xxviii. p. 260, 1840), recommends a solution of caustic potash for extracting the bitter taste of this lichen. A pound of carbonate of potash (rendered caustic by a pound of lime) is sufficient for 28 lbs. of the plant.]. But the subsequent washing will not remove the whole of the alkaline salt. Instead, therefore, of using an alkali, distilled water may be used to extract the bitter principle. The lichen should be heated once or twice in water up to about 180° F., by which the lichen will be deprived of most of its bitterness. It is then to be boiled in water or milk. When the decoction is sufficiently concentrated it gelatinizes on cooling. It may be flavoured with sugar, lemon peel, white wine, or aromatics, and then forms a very agreeable kind of diet.
DECOCTUM CETRARIAE, L. [U. S.]; Decoctum Lichenis Islandici, D.; Decoction of Iceland Moss.—(Iceland Moss 3v [℥j, D. (℥ss, U. S.)]; Distilled Water [Water, U. S.] Ojss; boil down to a pint, and strain.) Dose, f℥j to f℥iv every four hours.
The Elements of Materia Medica and Therapeutics, Vol. II, 3th American ed., was written by Jonathan Pereira in 1853.