This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Origin and Sensible Properties. Purging cassia consists of the fruit of Cassia Fistula (Cathartocarpus Fistula, Persoon), a large tree, indigenous in India and Upper Egypt, and introduced into the West Indies, whence our supplies of the medicine are derived. The fruit is a dark-brown, cylindrical, ligneous pod, a foot or more in length by less than an inch in diameter, straight or slightly curved. The pods hang in numbers on the tree, and produce a loud sound by striking against one another, when agitated by a high wind. In the interior, they are divided by transverse woody partitions into cells, which contain a blackish pulp surrounding the seeds, of which there is one in each cell.
Pulp of Purging Cassia (Cassiae Fistulae Pulpa, U.S. 1850; Cassia Praeparata, Lond.; Cassiae Pulpa, Ed.; Cassia, Br.) is the part of the pod used. When the pods are fresh, it may be scraped out with a knife; but, as they are usually brought to us, they contain the pulp dried upon the walls of the cells; and it is necessary to bruise them, and treat them with boiling water, in order to soften it. The pulp is then separated by straining through sieves. It is soft, blackish, of a slight rather unpleasant odour, and a sweet mucilaginous taste, often becoming acidulous through exposure. It contains sugar and gum; but its purgative principle has not been isolated. It is not directed as a distinct preparation, either in the present U. S. or the British Pharmacopoeia; being, in the former, prepared when wanted for use in the confection of senna; and, in the latter, constituting the primary medicine designated as cassia.
Cassia pulp is in small doses laxative, in larger purgative, and, when given very freely, is apt to produce nausea, flatulence, and griping. The passages themselves are unirritating. It might be used as a laxative in habitual costiveness, but is almost never given alone. The dose for an adult for laxative effect is one or two drachms, as a purgative one or two ounces.
A Confection (Confectio Cassia, Lond.) was directed by the London College, consisting of the pulps of cassia and tamarinds, manna, and the syrup of roses, the dose of which was about half an ounce for an adult. it has been omitted in the British Pharmacopoeia. in this country, the pulp is used almost exclusively as an ingredient of the confection of senna.