SEMEN LINI.

Botanical Origin—Linum usitatissimum L., Common Flax, is an annual plant, native of the Old World, where it has been cultivated from the remotest times. It sows itself as a weed in tilled ground, and is now found in all temperate and tropical regions of the globe. Heer regards it as a variety evolved by cultivation from the perennial L. angustifolium Huds.

History—The history of flax, its textile fibre and seed, is intimately connected with that of human civilisation. The whole process of converting the plant into a fibre fit for weaving into cloth is frequently depicted on the wall-paintings of the Egyptian tombs.[391] The grave-clothes of the old Egyptians were made of flax, and the use of the fibre in Egypt may be traced back, according to Unger,[392] as far as the 23rd century b.c. The old literature of the Hebrews[393] and Greeks contains frequent reference to tissues of flax; and fabrics woven of flax have actually been discovered together with fruits and seeds of the plant in the remains of the ancient pile-dwellings bordering the lakes of Switzerland.[394]

The seed in ancient times played an important part in the alimentation of man. Among the Greeks, Alcman in the 7th century b.c., and the historian Thucydides, and among the Romans Pliny, mention linseed as employed for human food. The roasted seed is still eaten by the Abyssinians.[395]

Theophrastus expressly alludes to the mucilaginous and oily properties of the seed. Pliny and Dioscorides were acquainted with its medical application both external and internal. The latter, as well as Columella, exhaustively describes flax under its agricultural aspect. In an edict of the Emperor Diocletian De pretiis rerum venalium[396] dating a.d. 301, linseed is quoted 150 denarii, sesamé seed 200, hemp seed 80, and poppy seed 150, the modius castrensis, equal to about 880 cubic inches.[397] The propagation of flax in Northern Europe as of so many other useful plants was promoted by Charlemagne.[398] It seems to have reached Sweden and Norway before the 12th century.[399]

Description—The capsule which is globose splits into 5 carpels, each containing two seeds separated by a partition. The seeds are of flattened, elongated ovoid form with an acute edge, and a slightly oblique point blunt at one end. They have a brown, glossy, polished surface which under a lens is seen to be marked with extremely fine pits. The hilum occupies a slight hollow in the edge just below the apex. The testa which is not very hard encloses a thin layer of albumen surrounding a pair of large cotyledons having at their pointed extremity a straight embryo. The seeds of different countries vary from ¼ to ⅙ of an inch in length, those produced in warm regions being larger than those grown in cold. We find that 6 seeds of Sicilian linseed, 13 of Black Sea and 17 of Archangel linseed weigh respectively one grain.

When immersed in water, the seeds become surrounded by a thin, slippery, colourless, mucous envelope, which quickly dissolves as a neutral jelly, while the seed slightly swells and loses its polish. The seed when masticated has a mucilaginous oily taste.

Microscopic Structure—On examining the testa under almond oil or oil of turpentine, the outlines of the epidermal cells are not distinctly visible. But under dilute glycerin or in water the epidermis quickly swells up to 3 or 4 times its original thickness; on warming, the entire epidermis is resolved into mucilage, except a thin skeleton of cell-walls, which withstands even the action of caustic lye. The formation of the mucilage may be conveniently studied by the use of a solution of ferrous sulphate, with which thin sections of the testa should be moistened. Other structural peculiarities may be seen if they are imbued with concentrated sulphuric acid, washed and then moistened with a solution of iodine. The application of polarized light is also useful. By the latter means crystalloid granules of albuminoid matter become visible if the sections are examined under oil. The tissue of the albumen and the cotyledons abounds in drops of fatty oil.

Chemical Composition—The constituent of chief importance is the fixed oil which the seed contains to about ⅓ of its weight. The proportion obtained by pressure on a large scale is 20 to 30 per cent. varying with the quality of the seed. The oil when pressed without heat and when fresh has but little colour, is without unpleasant taste, and does not solidify till cooled to -20° C. The commercial oil however is dark yellow, and has a sharp repulsive taste and odour. On exposure to the air, especially after having been heated with oxide of lead, it quickly dries up to a transparent varnish consisting chiefly of Linoxyn, C₃₂H₅₄O₁₁. The crude oil increases in weight 11 to 12 per cent., although at the same time its glycerin is destroyed by oxidation.

By saponification, linseed oil yields glycerin, and 95 per cent. of fatty acids, consisting chiefly of Linoleic Acid, C₁₆H₂₆O₂, accompanied by some oleic, palmitic, and myristic acid. The action of the air transforms linoleic acid into the resinoid Oxylinoleic Acid, C₁₆H₂₆O₅. Linoleic acid appears to be contained in all drying oils, notably in that of poppy seed. It is not homologous either with ordinary fatty acids or with the oleic acid of oil of almonds, C₁₈H₃₄O₂. The chemistry of the drying oils, especially those of linseed and poppy, has been particularly investigated by Mulder.[400]

The viscid mucilage of linseed cannot be filtered till it has been boiled. It contains in the dry state more than 10 per cent. of mineral substances, when freed from which and dried at 110° C. it corresponds, like althæa-mucilage, to the formula C₁₂H₂₀O₁₀. The seeds by exhaustion with cold or warm water afford of it about 15 per cent. By boiling nitric acid it yields crystals of mucic acid; by dilute mineral acids it is broken up into dextrogyre gum and sugar and cellulose.[401]

Linseed contains about 4 per cent. of nitrogen corresponding to about 25 per cent. of protein-substances. After expression of the oil these substances remain in the cake so completely that the latter contains 5 per cent. of nitrogen, and constitutes a very important article for feeding cattle.

In the ripe state linseed is altogether destitute of starch, though this substance is found in the immature seed in the very cells which subsequently yield the mucilage. The latter may be regarded as in analogous cases to be a product of the transformation of starch.

The amount of water retained by the air-dry seed is about 9 per cent.

The mineral constituents of linseed, chiefly phosphates of potassium, magnesium, and calcium, amount on an average to 3 per cent., and pass into the mucilage. By treating thin slices of the testa and its adhering inner membrane with ferrous sulphate, it is seen that this integument is the seat of a small amount of tannin.

Production and Commerce—Flax is cultivated on the largest scale in Russia, from which country there was imported into the United Kingdom in 1872 linseed to the value of 3 millions sterling. The shipments were made in about equal proportion from the northern and the southern ports of Russia.

The imports from India in the same year amounted in value to £1,144,942, and from Germany and Holland to £144,108. The total import in 1872 was 1,514,947 quarters, value £4,513,842.

The cultivation of flax in Great Britain appears to be declining. The area under this crop in 1870 was 23,957 acres; in 1871, 17,366 acres; in 1872, 15,357 acres; and in 1873, 14,683 acres. The last named area reckoning the yield at 2 to 2½ quarters of seed per acre would represent a production of about 30,000 to 38,000 quarters.

In English price-currents, eight sorts of linseed are enumerated, namely, English, Calcutta, Bombay, Egyptian, Black Sea and Azof, Petersburg, Riga, Archangel. The first three appear to fetch the highest prices.

Uses—In medicine, linseed is chiefly used in the form of poultice which may be made either of the seed simply ground or of the pulverized cake. In either case the powder should not be long stored, as the oil in the comminuted seed is rapidly oxidized and fatty acids produced. An infusion of the seeds called Linseed Tea is a common popular demulcent remedy.

Adulteration—Linseed is very liable to adulteration with other seeds, especially when the commodity is scarce. The admixture in question is due in part to careless harvesting and in part to intentional additions. In 1864 the impure condition of the linseed shipped to the English market had become so detrimental to the trade that the importers and crushers founded an association called The Linseed Association of London, by which they bound themselves to refuse all linseed containing more than 4 per cent. of foreign seeds, and this step very rapidly improved the quality of the article.[402]

As the druggist has to purchase linseed meal, he must of necessity rely to some extent on the character of the oil-presser from whom he derives his supplies. The presence of the seeds of Cruciferæ (as rape and mustard) which is common, may be recognized by the pungent odour of the essential oil which they develope in contact with water. The introduction of cereals would also be easily discovered by iodine, which strikes no blue colour in a decoction of linseed. The microscope will also afford important aid in the examination of linseed cake or meal.