All the aloes of commerce is derived from plants belonging to the genus Aloe, the leaves of which, on being wounded, yield a bitter purgative juice. The more prominent species from which the drug is derived are Aloe spicata growing at the Cape of Good Hope, Aloe Socotrina inhabiting the island of Socotra and probably the neighbouring coasts of Africa and Arabia, and Aloe vulgaris, a native of the South of Europe and North of Africa, and cultivated largely in the West' indies, particularly in the island of Barbadoes. Other species contribute to the aloes of commerce, but have attracted less notice than those mentioned. All the species are perennial, with fleshy and succulent leaves, the purgative juice of which is contained in passages underneath the epidermis, and flows out when the leaves are cut transversely. The parenchyma of the leaf yields on pressure a mucilaginous juice, which has little of the cathartic property.

Aloes is obtained from the plants by processes somewhat different, and varies in its quality according to the particular method followed. The best is prepared by cutting off the leaves, receiving the juice which exudes in a convenient receptacle, and then allowing it to evaporate in the sun. Another method, which affords also a good product, though somewhat inferior, is to inspissate the juice, collected as just mentioned, by artificial heat. A third plan is to bruise the leaves, express the juice, and boil it down to the proper consistence; and a fourth, simply to make a decoction with the comminuted leaves, and, having separated the undissolved matter, to concentrate by boiling as just mentioned. The last two methods yield the drug of inferior quality, and the fourth method is the worst of all.

There are several varieties of the drug, each characterized by peculiar qualities, and derived from a peculiar source. Of these it is necessary to mention here only the Cape aloes, the Socotrine, the hepatic, and the Barbadoes. They are brought into market, sometimes in skins, sometimes in chests, kegs, or barrels, and sometimes in gourds; but, as kept, in the shops, they are usually broken into fragments altogether irregular in size and form.

1. Cape Aloes

Aloe Capensis. U.S. This, which has been very largely consumed in the United States, and, when pure, is an excellent variety of the drug, received its name from the Cape of Good Hope, where it is prepared. it is said to be procured from different species of Aloe, of which, however, A. spicata probably yields it most abundantly. The juice, which flows from the leaves when cut, is boiled to the due consistence, and hardens on cooling. it is characterized by its dark-olive or greenish-black colour, its smooth and very glossy surface when broken, its translucency at the edges, and the fine bright-yellow colour of its powder, which is slightly tinged with green. The pieces are often more or less covered with this yellow powder, which tends to conceal their proper colour in mass. Small fragments are occasionally found in the packages which are almost transparent, and give a yellow or reddish tinge to transmitted light; and it is said that some parcels from the Cape have had a yellowish-brown colour like that of Socotrine aloes, which is very possible; as the drug is derived from different species. When perfectly solid it has little or no smell; but, when the powder is received into the nostrils, it produces, in minute quantity, an intense impression, which can scarcely be distinguished from the sense of bitterness which it also impresses on the palate. in hot weather the pieces are often soft, especially when recent; but they are hard and brittle when cold, and become so at all temperatures by time.

2. Socotrine Aloes

Aloe Socotrina. U. S., Br. This variety of aloes has been long known and most esteemed. it derives its name from the island of Socotra, in the Straits of Babelmandel, where it is produced; but it is highly probable that much of the drug, sold by this name, is obtained also from the neighbouring coast of Africa. it is supposed to be collected from A. Socotrina; the juice being allowed to inspissate in the sun. The pieces are of a yellowish-brown or reddish-brown colour, considerably resembling that of the liver. Not unfrequently the outside of the pieces is reddish-brown, while the interior is yellowish, and portions at first light-coloured become darker by exposure. its fractured surface is shining, though less so than that of the preceding variety. The edges are translucent. it has an agreeable aromatic odour, which is quite peculiar; and its powder, which is of a beautiful golden-yellow colour, affects the nostrils in the same manner as that of the Cape aloes. Like that variety, it is apt to be soft when fresh, and especially in the interior of the masses, but hardens by time and exposure.

3. Hepatic Aloes

Aloe Hepatica. Lond., Dub. - Aloe indica. Ed. Hepatic aloes derives its name from the resemblance of its colour to that of the liver. But, in this respect, it differs little from the darker-coloured portions of the Socotrine. it is brought from the East indies, especially Bombay, whither it is taken from the coast of Arabia, and probably of Africa. it may possibly be obtained from the same species as the Socotrine, and differ from that variety simply from its less careful preparation; but nothing is known positively upon these points. it is of a reddish-brown colour, sometimes very dark, less shining than the preceding varieties, quite opaque at the edges, and of a disagreeable instead of aromatic odour. The colour of the powder is dull-yellow. This variety often contains impurities. it is not at present officinally recognized, having been abandoned in the British Pharmacopoeia, and never occupied a place in ours.

4. Barbadoes Aloes

Aloe Barbadensis. U.S., Br. This derives its name from the island of Barbadoes, where it is most largely produced, though collected also in Jamaica, and perhaps other West India islands. it is said to be obtained mainly from Aloe vulgaris, which is cultivated for the sake of it. Either the juice of the leaves, or a decoction obtained by boiling them, finely chopped, and suspended in nets or baskets in water, is evaporated sufficiently, and then poured into large gourds to harden. This variety is of a dark-brown or reddish-brown colour of different shades, of a dull fracture, perfectly opaque at the edges, and of a disagreeable nauseous odour. The colour of the powder is dull-yellow, with a tinge of olive. it is said to be the strongest in cathartic power, and is much used as a purgative for horses.