_Fucus Hibernicus_; _Carrageen_,[2770] _Irish Moss_; F. _Mousse
d’Irlande_, _Mousse perlée_; G. _Knorpeltang_, _Irländisches Moos_,
_Perlmoos_.
=Botanical Origin=—_Chondrus crispus_ Lyngbye (_Fucus crispus_ L.),
a sea weed of the class _Florideæ_, abundant on rocky sea-shores of
Europe from the North Cape to Gibraltar; not frequent however in the
Baltic, and altogether wanting in the Mediterranean, but largely met
with on the eastern coasts of North America.
=History=—_Chondrus crispus_ was figured in 1699 by Morison,[2771] yet
only Todhunter at Dublin introduced it to the notice of the medical
profession in England in 1831, and shortly afterwards it attracted some
attention in Germany. It was never admitted to the London or British
pharmacopœia, and is but little esteemed in medicine.
=Description=—The entire plant is collected: in the fresh state it is
soft and cartilaginous, varying in colour from yellowish-green to livid
purple or purplish-brown, but becoming, after washing and exposure
to the sun, white or yellowish, and when dry, shrunken, horny and
translucent.
The base is a small flattened disc, from which springs a frond
or thallus 4 to 6 inches or more in length, having a slender
subcylindrical stem, expanding fan-like into wedge-shaped segments,
of very variable breadth, flat or curled, and truncate, emarginate or
bifid at the summit.
The fructification[2772] consists of tetraspores or cystocarps, rising
but slightly from the substance of the thallus, and appearing as little
wart-like protuberances.
In cold water, carrageen swells up to its original bulk, and acquires
a distinct seaweed-like smell. A quantity of water equal to 20 or
30 times its weight, boiled with it for ten minutes, solidifies on
cooling to a pale mawkish jelly.
[2769] _Etude sur l’Ergot du Diss_, Alger et Paris, 1863; _Journ. de
Pharm._ i. (1865) 444.
[2770] _Carrageen_ in Irish signifies _moss of the rock_. We learn from
an Irish scholar that it would be more correctly written _carraigeen_.
[2771] _Plantar. hist. universal._ Oxon. iii. tab. 11.
[2772] See Luerssen (quoted at p. 734) i. 124 _et seq._
=Microscopic Structure=—The tissue of _Chondus crispus_ is made up of
globular or elongated, thick-walled cells. The superficial layers on
both sides of the lobes constitute a kind of peel, easily separable in
microscopic sections. The interior or medullary part exhibits a much
less densely packed tissue formed of larger cells. The larger cavities
of this tissue contain a granular mucilaginous matter, assuming a
slight violet tinge on addition of iodine. In water however, the
cell-walls swell up so as to form a gelatinous mass, in which separate
cells can at last be scarcely distinguished.[2773] In the fresh state,
its cells also contain granules of chlorophyll imbued with a red
matter, termed _Phyco-erythrin_. But by washing and exposure to the
air, these colouring substances are removed or greatly altered, and are
no longer visible in the commercial drug.
=Chemical Composition=—The constituents of carrageen are those
generally found in marine algæ, especially as regards the mucilage.
This latter is insoluble in an ammoniacal solution of copper
(Schweizer’s test); by the action of fuming nitric acid, it yields,
in common with gum, an abundance of mucic acid. The mucilage of
carrageen, like many similar bodies, obstinately retains inorganic
matter; after it had three times been dissolved in water, and as many
times precipitated with alcohol, we found it still to yield the same
quantity of ash as the raw drug itself, that is to say, more than 15
per cent. The mucilage, perfectly dried, is a tough horny substance, of
a greyish colour; it quickly swells up in water, forming a jelly which
is precipitable by neutral acetate of lead.
By boiling carrageen for a week with water containing 5 per cent.
of sulphuric acid, Bente (1876) obtained crystals of _lævulinic
acid_, C₅H₈O₃, and an amorphous sugar. The former is also afforded by
cellulose of pine wood and by paper.
According to Blondeau,[2774] the mucilage of carrageen contains 21 per
cent. of nitrogen and 2·5 of sulphur, a statement which we are able to
point out as erroneous. We find in it no sulphur, and only 0·88 per
cent. of nitrogen. The drug itself yielded us not more than 1·012 per
cent. of nitrogen.
When thin slices of the plant are treated with alcoholic potash, and
then after washing left for 24 hours in contact with a solution of
iodine in potassium iodide, they acquire a deep blue; yet, starch
granules are not found in this seaweed. Lastly in connexion with
carrageen may be mentioned _Fucusol_, an oily liquid isomeric with
furfurol, obtained by boiling seaweeds with dilute sulphuric acid.
=Commerce=—The plant is collected on the west and north-west coast
of Ireland: Sligo is said to be a great depôt for it. Carrageen of
superior quality is sometimes imported from Hamburg.
[2773] Alcohol, glycerin or a fatty oil are the liquids most suited for
the microscopic examination of this drug.
[2774] _Journ. de Pharm._ ii. (1865) 159.
The largest quantities of carrageen, sometimes half a million pounds
a year, are gathered near Minot Ledge lighthouse, Scituate, Plymouth
county, on the coast of Massachusetts, where a systematic process of
preparing it for the market is adopted.[2775]
=Uses=—The mucilaginous decoction and jelly which carrageen affords are
popular remedies in pulmonary and other complaints; but as nutriment
such preparations are much over-estimated.[2776]
Carrageen is sometimes used for feeding cows and calves; and under the
name of _Alga marina_, for stuffing mattresses. It is largely used
for industrial purposes, like other mucilaginous matter. Its mucilage
serves for thickening the colours employed in calico-printing, and as
size for paper and for cotton goods. In America it is used for fining
beer.
=Substitutes=—_Gigartina mammillosa_[2777] J. Agardh (_Chondrus
mammillosus_ Grev.) is collected indiscriminately with _Ch. crispus_.
It is distinguished from the latter chiefly by having the flat portion
of the thallus beset with elevated or stalked tubercles, bearing the
cystocarps; but it has the same properties. _G. acicularis_ Lamouroux,
a species common on the coasts of France and Spain, and having slender
cylindrical branches, is occasionally collected along with _Chondrus
crispus_. Dalmon (1874) who has examined it, asserts it to be less
soluble in boiling water than true carrageen. Small quantities of other
seaweeds are often present through the negligence of the collectors.