Under the name of fetid, caballine, or horse aloes, inferior varieties of the drug have been brought into commerce from various sources; but, not being used in medicine, they need not be described here.

Sensible and Chemical Properties. All the varieties of aloes are extremely and disagreeably bitter, and all, in powder, produce the peculiar impression on the nostrils before referred to under Cape aloes. Their other sensible properties have been already sufficiently described. Heated in the open air, aloes takes fire, and gives out while burning thick fumes, which have the odour of the drug. it imparts a dark yellowish-brown colour, with its bitter taste and medical virtues, to water and alcohol. it consists of a portion soluble in cold water, and of another insoluble, in the former of which the sensible and medicinal properties of the drug reside. Alcohol and boiling water dissolve nearly the whole; but the latter deposits a large proportion on cooling. It has been ascertained that, at an elevated temperature, and exposed to the air, the soluble portion in solution attracts oxygen from the atmosphere, and becomes insoluble and inert. Hence, the longer the juice of the plant is exposed to heat in its inspissation, the weaker it becomes; and hence, too, the impropriety of exposing aloes long to a boiling temperature in its pharmaceutical treatment. The proportion of this soluble matter differs very much in different varieties of the drug, but is greatest in the Socotrine, of which the finest specimens have yielded as much as 85 per cent. From this proportion it diminishes, in the inferior kinds, down to about 50 per cent. The portion soluble in cold water and alcohol has been called extractive matter; that soluble only in alcohol or boiling water, resin or more properly apotheme; and, besides these, there is said to be a proportion of albumen. Volatile oil has been found in Socotrine aloes. The alkalies, their carbonates, and soap render the insoluble part more soluble in water. The infusion of galls yields a copious precipitate with an infusion of aloes, and is therefore incompatible.

Active Principle. The soluble matter above referred to, under the name of extractive, contains, but is not itself the pure active principle. M. Edmund Robiquet supposed that he had isolated this principle, and gave it the name of aloesin. But subsequent investigation has shown that this was not pure. Messrs. T. and H. Smith, of Edinburgh, have succeeded in completely isolating the active principle, and obtaining it in a crystalline state. They have named it aloin. For the mode of procuring it, the reader is referred to the article Aloes, in the U. S. Dispensatory (11th or 12th ed.). Aloin is a neuter substance, in pale yellow crystals, at first sweetish but soon becoming intensely bitter to the taste, combustible without residue, somewhat soluble in cold water and alcohol, but more so in those liquids when hot, rendered more soluble by the alkalies, and rapidly oxidized in a heated solution exposed to the air. It is precipitated by a strong solution of Subacetate of lead, in combination with the oxide. It operates as a cathartic in the dose of one or two grains, and sometimes in so small a dose as half a grain.

Effects on the System

Aloes is a warming somewhat stimulant cathartic, with a disposition to act preferably on the large intestines, very slow in its operation, and possessing, in addition to its purgative properties, those of a tonic, hepatic stimulant, and emmenagogue. In the dose of a grain or two, repeated two or three times a day, it generally produces one or more evacuations in the twenty-four hours, and exercises a tonic influence on the digestive organs, more particularly exhibited in debilitated states of the stomach. If continued long, it evinces a tendency to irritate the rectum, and, indeed, to cause a congested state of the pelvic viscera generally, which gives rise to tenesmus, feelings of heat, weight, or uneasiness in the parts sometimes extending to the lower limbs, and occasionally excitation of the sexual organs, a disposition to micturate frequently, and with women an increase of the menstrual function. in full doses, it acts vigorously as a cathartic, and generally produces more or less of the above-mentioned effects in the pelvic region, especialy heat and irritation of the rectum, though, in the great majority of cases, not to any painful extent. At the same time, it increases somewhat the frequency of the pulse, and the general warmth. The cathartic effect is seldom produced before six hours after the dose has been taken, frequently not until from eight to twelve hours, and sometimes even after twenty-four. The discharges are feculent, and generally more or less consistent; as it is the contents of the lower bowels that are evacuated. Little or no increase of cathartic effect can be obtained by a further increase of the dose; as nothing is left in the lower colon and rectum to be discharged, and the purgative action of the medicine does not extend to the upper bowels; but the irritation of the pelvic viscera is augmented in proportion to the quantity taken. The operation would seem to be directed mainly to the peristaltic function; as the secretions of the bowels are not materially increased. it is asserted, however, by some, that the hepatic secretory function is excited, and bile produced more copiously than in health.

Mode of Operation

There can, I think, be little doubt that aloes is absorbed, and produces its peculiar effects mainly through the circulation. Thus, it has been asserted that, when given as an enema, it does not, like most irritants in the same situation, produce a speedy evacuation of the bowels; but acts as slowly, and in the same manner, as when taken by the mouth. This could not happen, if, in its ordinary method of operation, it affected the rectum only upon reaching it with the contents of the bowels. But still stronger proof is afforded by the well attested fact, that, when sprinkled on blistered surfaces deprived of the cuticle, it acts after the same interval of time, upon the same portion of the bowels, and, so far as can be appreciated, in the same manner, as when swallowed. This could only happen through its absorption. it seems, then, when taken into the circulation, to be capable of moderately exciting the heart and arteries, increasing the action of the liver, and specially stimulating the whole pelvic viscera.