3. Fucus vesiculosus, Linn.—Common Sea Wrack.
History.—Theophrastus [Hist. Plant. lib. iv. cap. vii.] mentions several species of Algae (φυκος). Fucus vesiculosus is sometimes termed quercus marina, bladder fucus, and common sea-ware, kelpware, and black tang.
Botany. Gen. Char.—Frond linear, either flat, compressed, or cylindrical, dichotomous (rarely pinnated), coriaceous. Airvessels [vesiculae] when present innate, simple. Receptacles either terminal or lateral, filled with mucus, traversed by a net-work of jointed fibres, pierced by numerous pores, which communicate with immersed spherical conceptacles, containing parietal spores, or antheridia, or both (Harvey).
Sp. Char.—Frond plane, linear, dichotomous, entire at the margin. Air-vessels roundish-oval in pairs. Receptacles mostly elliptical, terminating the branches (Greville).
Very variable; but the varieties pass so insensibly into each other that it is difficult to define them strictly.
Hab.—Sea-shores. Very common everywhere.
Physical Properties.—Its substance is thickish, flexible, but very tough. Its colour is dark, olivaceous, glossy green, paler at the extremities, and becomes black by drying. Its odour is strong; its taste nauseous.
Composition.—It has been analyzed by Stackhouse [Dict. Scien. Nat. xviii. 500.], by Gaultier de Claubry [Ann. Chim. xciii. 116], by John [Schweigger's Journ. xiii. 464.], and by Fagerstrom [Gmelin, Handb. d. Chem. Bd. ii. S. 1354.]. The following appear to be its constituents: Cellulose, mucilage (carrageenin), mannite, odorous oil, colouring and bitter matters, and various salts. The following table shows the composition and proportion of ash of Fucus vesiculosus of different localities:—
||Mouth of the Clyde||Mouth of the Mersey||North Sea.||Denmark.||Greenland.||Mean.|
|Chloride of sodium||25.10||9.89||35.38||3.53||25.93||19.82|
|Iodide of sodium||0.37||
|Phosphate of iron and phosphate of lime||2.99||
|Oxide of iron||0.33||4.42||
||100 ||100 ||100 ||100 ||100 ||100|
|Per centage of ash (calculated dry)||16.39||13.22||20.56||
 Gödechens, Annal. der Chemie und Pharm. liv. p. 532.  James, ibid.  Schweitzer.  Forchhammer.]
Chemical Characteristics.—By treating the distilled water of Fucus vesiculosus with ether, a semi-solid white oil is extracted, which is the odorous principle. The aqueous decoction of this plant is neutral, and contains in solution mucilage (see carrageenin) and various salts. It yields, with chlorine and starch, faint traces only of iodine, sometimes none at all. But if alcohol be added, by which the mucilage and a part of the sulphates are thrown down, the alcoholic liquor evaporated, and the residue mixed with potash, then calcined, and afterwards treated with hydrochloric acid to disengage hydrosulphuric acid, we may sometimes detect iodine in the filtered liquor by the deep blue colour formed on the addition of starch and chlorine [Guibourt, Hist. des Drog. 4me éd. ii. 46.].
By combustion in the open air, this plant yields the ash called kelp; and by incineration in a covered crucible it gives a charcoal, termed vegetable ethiops.
Physiological Effects.—During the winter, in some of the Scottish islands, horses, cattle, and sheep are fed on it [Greville, Algae Brit. xx.]. Its local action is detergent, and, perhaps, discutient. Its remote effects are probably analogous to those caused by small doses of iodine, modified by the influence of salts of sodium and calcium.
Uses.—Frictions of the plant, with its contained mucilage, were employed, with supposed advantage, by Dr. Russell [Dissertation on the Use of Sea Water, 5th ed. 1769, pp. 41 and 44.], in glandular enlargements and other scrofulous tumours: the parts were afterwards washed with sea water. He also gave internally the expressed juice of the vesicles in glandular affections [Op. cit. p. 99.].
AETHIOPS VEGETABILIS; Vegetable Ethiops.—This is prepared by incinerating Fucus vesiculosus in a covered crucible. It is composed of charcoal and various salts (see supra). When hydrochloric acid is added to it, traces of sulphuretted hydrogen are frequently evolved. By digesting the ethiops in water, and testing the solution with nitric acid and starch, I have sometimes failed to obtain the blue colour indicative of the presence of iodine. It has been exhibited in bronchocele and scrofulous maladies. Dr. Russell [Op. cit. p. 98] says it far exceeds burnt sponge in virtue. It has been employed also as a dentifrice. The dose of it is from ten grains to two drachms.