1911 Encyclopædia Britannica/Aloe

ALOE, a genus of plants belonging to the natural order Liliaceae, with about 90 species growing in the dry parts of Africa, especially Cape Colony, and in the mountains of tropical Africa. Members of the closely allied genera Gasteria and Haworthia, with a similar mode of growth, are also cultivated and popularly known as aloes. The plants are apparently stemless, bearing a rosette of large, thick, fleshy leaves, or have a shorter or longer (sometimes branched) stem, along which, or towards the end of which and its branches, the generally fleshy leaves are borne. They are much cultivated as ornamental plants, especially in public buildings and gardens, for their stiff, rugged habit. The leaves are generally lance-shaped with a sharp apex and a spiny margin; but vary in colour from grey to bright green, and are sometimes striped or mottled. The rather small tubular yellow or red flowers are borne on simple or branched leafless stems. and are generally densely clustered. The juice of the leaves of certain species yields aloes (see below). In some cases, as in Aloe venenosa, the juice is poisonous. The plant called American aloe, Agave Americana (q.v.), belongs to a different order, viz. Amaryllidaceae.

Aloes is a medicinal substance used as a purgative and produced from various species of aloe, such as A. vera, vulgaris, socotrina, chinensis, and Perryi. Several kinds of aloes are distinguished in commerce—Barbadoes, Socotrine, hepatic, Indian, and Cape aloes. The first two are those commonly used for medicinal purposes. Aloes is the expressed juice of the leaves of the plant. When the leaves are cut the juice flows out, and is collected and evaporated. After the juice has been obtained, the leaves are sometimes boiled, so as to yield an inferior kind of aloes.

From these plants active principles termed aloins are extracted by water. According to W. A. Shenstone, two classes are to be recognized: (1) Nataloins, which yield picric and oxalic acids with nitric acid, and do not give a red coloration with nitric acid; and (2) Barbaloins, which yield aloetic acid, C₇H₂N₂O₅, chrysammic acid, C₇H₂N₂O₆, picric and oxalic acids with nitric acid, being reddened by this reagent. This second group may be divided into α-Barbaloins, obtained from Barbadoes aloes, and reddened in the cold, and β-Barbaloins, obtained from Socotrine and Zanzibar aloes, reddened by ordinary nitric acid only when warmed, or by fuming acid in the cold. Nataloin, 2C₁₇H₁₈O₇⋅H₂O, forms bright yellow scales, melting at 212°–222°; barbaloin, C₁₇H₁₈O₇, forms yellow prismatic crystals. Aloes also contain a trace of volatile oil, to which its odour is due.

The dose is 2 to 5 grains, that of aloin being 1/2 to 2 grains. Aloes can be absorbed from a broken surface and will then cause purging. When given internally it increases the actual amount as well as the rate of flow of the bile. It hardly affects the small intestine, but markedly stimulates the muscular coat of the large intestine, causing purging in about fifteen hours. There is hardly any increase in the intestinal secretion, the drug being emphatically not a hydragogue cathartic. There is no doubt that its habitual use may be a factor in the formation of haemorrhoids; as in the case of all drugs that act powerfully on the lower part of the intestine, without simultaneously lowering the venous pressure by causing increase of secretion from the bowel. Aloes also tends to increase the menstrual flow and therefore belongs to the group of emmenagogues. Aloin is preferable to aloes for therapeutic purposes, as it causes less, if any, pain. It is a valuable drug in many forms of constipation, as its continual use does not, as a rule, lead to the necessity of enlarging the dose. Its combined action on the bowel and the uterus is of especial value in chlorosis, of which amenorrhoea is an almost constant symptom. The drug is obviously contraindicated in pregnancy and when haemorrhoids are already present. Many well-known patent medicines consist essentially of aloes.

The lign-aloes is quite different from the medicinal aloes. The word is used in the Bible (Numb. xxiv. 6), but as the trees usually supposed to be meant by this word are not native in Syria, it has been suggested that the LXX. reading in which the word does not occur is to be preferred. Lign-aloe is a corruption of the Lat. lignum-aloe, a wood, not a resin. Dioscorides refers to it as agallochon, a wood brought from Arabia or India, which was odoriferous but with an astringent and bitter taste. This may be Aquilaria agallochum, a native of East India and China, which supplies the so-called eagle-wood or aloes-wood, which contains much resin and oil.