_Iceland Moss_; F. _Lichen ou Mousse d’Islande_; G. _Isländisches Moos_.
=Botanical Origin=—_Cetraria islandica_ Acharius.[2738]—It is abundant
in high northern latitudes, as Greenland, Spitzbergen, Siberia,
Scandinavia and Iceland, where it grows even in the plains. It is
found in the mountainous parts of Great Britain, France, Italy, and
Spain, in Switzerland (in elevations of nearly 10,000 feet), and in the
Southern Danubian countries. It also occurs in North America and in the
Antarctic regions.
=History=—In the North of Europe, this lichen has long been used
under the general name of _Mosi_, _Mossa_ or _Mus_,[2739] as an
article of food. It is the _Muscus crispæ Lactucæ similis_ of
Valerius Cordus,[2740] and was also mentioned by Ole Borrich, of
Copenhagen (1671), who called it _Muscus catharticus_, under the
notion that in early spring it possesses purgative properties.[2741]
The pharmaceutical tariff of the same city, of the year 1672,
likewise quotes _Muscus catharticus islandicus_.[2742] Its medicinal
employment in pulmonary disorders was favourably spoken of by Hjärne in
1683,[2743] but it is only since 1757 that it has come into general use
as a medicine, chiefly on the recommendation of Linnæus and Scopoli.
=Description=[2744]—The plant consists of an erect, foliaceous,
branching thallus, about 4 inches high, curled, channelled or rolled
into tubes, terminating in spreading truncate, flattened lobes, the
edges of which are fringed with short thick prominences. The thallus is
smooth, grey, or of a light olive-brown; the under surface is paler and
irregularly beset with depressed white spots. The apothecia (fruits),
which are not very common, appear at the apices of the thallus, as
rounded boss-like bodies, ²/₁₀ to ³/₁₀ of an inch across, of a dark,
rusty colour. The colour and mode of division of the thallus vary
greatly, so that many varieties of the plant have been distinguished.
[2738] _Cetraria_ from _cetra_, an ancient shield of hide, in allusion
to the circular apothecia.
[2739] These names are generally applied in Scandinavia and Iceland to
the smaller cryptogams, as lichens, true mosses, lycopodium, etc.
[2740] Hist. stirpium, quoted in the Appendix.
[2741] Bergius, _Materia Medica_, Stockholm, ii. (1778) 856.
[2742] Flückiger, _Documente_, quoted at page 404.
[2743] Murray, _Apparatus Medicaminum_, v. (1790) 510.
[2744] For an exhaustive account and figures see Luerssen (quoted at p.
734) p. 176.
In the dry state, Iceland moss is light, harsh and springy; it absorbs
water in which it is placed to the extent of a third of its weight,
becoming soft and cartilaginous; it ordinarily contains about 10 per
cent. of hygroscopic water. It is inodorous, but when wetted has a
slight seaweed-like smell; its taste is slightly bitter.
=Microscopic Structure=—A transverse section exhibits, when strongly
magnified, a broad loose central layer of long, thick-walled branching
walls of _hyphæ_, containing air, and enclosing wide hollow spaces.
This middle layer encloses a certain number of larger cells called
_gonidia_, coloured with chlorophyll. The gonidia are not destroyed
either by strong sulphuric acid, or by boiling them with potash. They
assume however a deep violet colour when treated with caustic potash
and then left for 24 hours in a solution of iodine in potassium iodide.
The tissues on either side of this central layer consists of very
thickly felted hyphæ, without intervening spaces, and does not appear
to contain any particular substance. This compact and tenacious tissue
passes into a thin cortical layer consisting of cells very closely
bound together. Under the influence of reagents this layer becomes very
evident: thus when moistened with strong sulphuric or hydrochloric
acid, it separates from the rest of the tissue as a coherent membrane,
and rolls itself backward. On boiling with water the inner tissue
swells up, the cell-walls being partly dissolved. Thin slices of
the lichen are coloured reddish or pale blue by iodine water,—more
distinctly blue, if previously treated with sulphuric acid. The colour
spreads uniformly over the inner tissue, but no starch granules can
be detected; the cortical layer is merely coloured brown by iodine.
The white spots on the outer surface of the thallus are resolved by
pressure under a plate of glass into minute round transparent granules,
not coloured by iodine, and thick branched cells like those of the
central layer.
The short thick prominences on the edge of the thallus, frequently
terminate in one or more sac-like cavities (_spermogonia_) containing
a large number of simple bar-shaped cells (_spermatia_), only 6 mkm.
long; they are enveloped in transparent mucus, and may be expelled
by pressure under glass. It has been shown by Stahl (1874) that
they represent the fertilizing corpuscles or seaweeds of the class
_Florideæ_.
The observations of De Bary (1866) and Schwendener (1867-70) confirmed
and much extended by the researches of Bornet[2745] (1873-74), have
shown that the gonidia of lichens are referable to some species of
_Alga_, and are capable of an independent existence; that the relations
of the hyphæ to the gonidia are of such a nature as to exclude the
possibility of either of those bodies being produced by the other;
and further that the theory of parasitism is the only one capable
of explaining these relations in a satisfactory manner. Under this
singular theory, lichens are compound organisms, formed of an alga, and
of a fungus living upon it as a parasite.
[2745] _Recherches sur les gonidies des Lichens._—_Ann. des Sciences
nat._ Bot. xvii. (1873) 45-110; 11 plates; also xix. (1874)
314-320.—For a complete abstract of these and all the more recent
investigations on this subject, see Luerssen (_l.c._) 186 _et seq._
=Chemical Composition=—Boiling water extracts from Iceland 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 decoction 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, C₁₂H₂₀O₁₀,
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
ammoniacal 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.[2746] The very 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 Knop and Schnedermann as _Thallochlor_; its
quantity is extremely small.
The bitter principle of Cetraria, called _Cetraric Acid_ or _Cetrarin_,
C₁₈H₁₆O₈, 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_, C₁₄H₃₄O₃, the crystals of
which melt at 120° C. The _Lichenic Acid_ found by Pfaff 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.[2747] None is exported from Iceland.
[2746] The various mucilages and gums yield from 4 to 20 per cent. of
ash, but lichenin yields _none_.
[2747] _Cat. of Spanish Productions_,—London Exhibition, 1851.
=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 flour used in making the _grout_ or grain soup. Occasionally it
is taken boiled in milk. It is not given, as has been asserted, to
domestic animals.
An interesting application of Iceland moss has recently been tried in
Sweden. Sten-Stenberg treats it with sulphuric or hydrochloric acid,
when 72 per cent. of grape sugar are formed, which may be converted
into alcohol.[2748]