Wellstead, who travelled in Socotra in 1833,[2553] says that in old times the aloë was far more largely grown there than at present, and that the walls which enclosed the plantations may still be seen. He adds that the produce was a monopoly of the Sultan of the island. At the present day the few productions of Socotra that are exported are carried by the Arab coasting vessels, coming annually from the Persian Gulf to Zanzibar, at which place they are transshipped for Indian and other ports. Dr. Kirk, who has resided at Zanzibar from 1866 to 1873, informs us that aloes from Socotra arrives in a very soft state packed in goatskins. From these it is transferred to wooden boxes, in which it concretes, and is shipped to Europe and America. To avoid loss the skins have to be washed; and the aloetic liquor evaporated.
Ligon,[2554] who visited the island of Barbados in 1647-50, that is about twenty years after the arrival of the first settlers, speaks of the aloë as if it were indigenous, mentioning also the useful plants which had been introduced. At that period the settlers knew how to prepare the juice for medicinal use, but had not begun to export it. Barbados aloes was in the drug warehouses of London in 1693.[2555]
The manufacture of aloes in the Cape Colony of South Africa was observed by Thunberg in 1773 on the farm of a boer named Peter de Wett, who was the first to prepare the drug in that country.[2556] Cape Aloes is enumerated in the stock of a London druggist in 1780, its cost being set down as £10 per cwt. (1s. 9½d. per lb.).
A new and distinct sort of aloes, manufactured in the colony of Natal, appeared in English commerce in 1870. It will be described further on.
Lignum Aloes—It is important to bear in mind that the word Aloes or Lign Aloës, in Latin Lignum Aloës, is used in the Bible and in many ancient writings to designate a substance totally distinct from the modern Aloes, namely the resinous wood of Aquilaria Agallocha Roxburgh, a large tree[2557] of the order Thymeleaceæ, growing in the Malayan Peninsula. Its wood constituted a drug[2558] which was, down to the beginning of the present century, generally valued for use as incense, but now esteemed only in the East.
Structure of the Leaf—The stout fleshy leaves of an aloë have a strong cuticle and thick-walled epidermis. Their interior substance is formed of very loose, large-celled, colourless pulp, traversed by vascular bundles, which, on transverse section, are seen to be accompanied by a group of large thin-walled cells[2559] containing the bitter juice which constitutes the drug under notice. These cells, on a longitudinal section, are seen to be considerably elongated, adjoining a single row of smaller, prismatic, truncated cells,[2560] by which the former are separated from the cortical layer. The prismatic cells contain a yellow juice, apparently different from that which yields aloes. The cortical tissue is filled with granules of chlorophyll, and exhibits between the cells groups of needles of calcium oxalate. Similar crystals are also found sparingly in the pulp.
The transparent pulp-tissue[2561] is rich in mucilage, which after dilution with water is precipitated by neutral acetate of lead, but is not coagulated by boiling.
The amount of bitter principles in the leaf probably varies with the age of the latter and with the season of the year. Haaxman mentions that, in Curaçao, the maximum is found when the leaves are changing from green to brown.
Cultivation and Manufacture—In Barbados,[2562] where Aloë vulgaris is systematically cultivated for the production of the drug, the plants are set 6 inches apart, in rows which are 1 to 1½ foot asunder, the ground having been carefully prepared and manured. They are kept free from grass and weeds, but yams or pulse are frequently grown between them. The plants are always dwarf, never in the least degree arborescent; almost all of those above a year old bear flowers, which being bright yellow, have a beautiful effect. The leaves are 1-2 feet long; they are cut annually, but this does not destroy the plant, which, under good cultivation, lasts for several years.
The cutting takes place in March and April, and is performed in the heat of the day. The leaves are cut off close to the plant, and placed very quickly, the cut end downwards, in a V-shaped wooden trough, about 4 feet long and 12 to 18 inches deep. This is set on a sharp incline, so that the juice which trickles from the leaves very rapidly flows down its sides, and finally escapes by a hole at its lower end into a vessel placed beneath. No pressure of any sort is applied to the leaves. It takes about a quarter of an hour to cut leaves enough to fill a trough. The troughs are so distributed as to be easily accessible to the cutters. Their number is generally five; and by the time the fifth is filled, the cutters return to the first and throw out the leaves, which they regard as exhausted. The leaves are neither infused nor boiled, nor is any use afterwards made of them except for manure.