Source, Etc

Cascara sagrada is the bark of Rhamnus Purshianus, de Candolle (N.O. Rhamneoe), a shrub or small tree abundant in North California and in the States of Washington and Oregon, the bark being collected in these States and exported from San Francisco. The bark of R. californicus, Eschscholz, was known to the Spanish settlers in California as cascara sagrada, a name which has since been applied to the bark of the closely allied R. Purshianus. The latter has been much used as a laxative since 1883.

The bark is collected in the spring and early summer, and dried in the shade; if left till later in the year it adheres so firmly to the wood that it has to be cut off, and then brings shavings of wood with it.

Description

Cascara sagrada occurs in straight, stiff, single quills or in channelled pieces. The quills vary from 5 to 25 mm. or more in diameter, whilst the channelled or sometimes flattish pieces may be as much as 10 cm. wide; commonly the drug is seen in pieces about 10 to 20 cm. long, 2 cm. wide, and from 1.5 to 4 mm. thick, the thinnest being most esteemed.

The outer layer is a smooth, dark purplish brown cork marked with transversely elongated whitish lenticels. The bark, however, is usually more or less completely covered with silvery grey patches of lichens which conceal the purple cork and the lenticels and give to the drug its pervading greyish white colour. The inner surface is of a dark, or even very dark, reddish brown colour and longitudinally striated, with faint transverse corrugations.

The fracture is short, that of the bast being shortly fibrous. The section exhibits under the lens a narrow purplish cork, a yellowish grey cortex in which darker translucent points (groups of scleren-chymatous cells) can be distinguished, and a brownish yellow bast in which wavy, somewhat distant medullary rays may sometimes be discerned.

The bark has a characteristic though not strong odour, and a persistent, nauseously bitter taste.

Like alder buckthorn bark, this drug should be kept for at least a year before it is used medicinally; the action is then milder and less emetic. It also shares with alder buckthorn bark the property of imparting a yellow colour to the paper in which it is kept.

Microscopical Characters

The structure of cascara sagrada closely resembles that of alder buckthorn bark, the chief differences being in the contents of the cork cells which are reddish brown, and the presence of groups of sclerenchymatous cells in the cortex and secondary bast.

The student should observe

(a) The purplish cork and the grey lichens covering it,

(b) The groups of sclerenchymatous cells in the cortex,

(c) The characteristic odour and taste; and should compare the bark with

Fig. 126.   Cascara Sagrada bark. Natural size.

Fig. 126. - Cascara Sagrada bark. Natural size.

Alder Buckthorn hark, which has deep crimson inner cork layers and no sclerenchymatous cells.

Constituents

Our knowledge of the constituents of cascara sagrada is very deficient. The presence of emodin and an allied substance, possibly frangula-emodin, has been definitely proved, but the latest research (Jowett, 1904) failed to afford any evidence of chrysophanic acid, chrysarobin, or any glucoside yielding by hydrolysis emodin, chrysophanic acid, or rhamnetin. The total amount of emodin and frangula-emodin (1.4 to 2.0 per cent.) present in the bark either normally or after boiling with dilute sulphuric acid is quite insufficient to account for the purgative action of the drug, and the real laxative principle remains therefore still unknown.

The presence of emodins may be demonstrated by the test given under Alder Buckthorn bark; the ammonia acquires a yellowish red colour.

The bitter taste of the bark appears to be due to a lactone which is converted into less bitter salts by treatment with alkalies or alkaline earths, but this change is accompanied by simultaneous loss of activity.

The bark also contains fat (about 2 per cent.), glucose, and a hydro-lytic enzyme. No difference could be detected in the chemical constituents of the fresh (one year old) bark and the matured (three years old) bark. Purshianin (Dohme) and cascarin (Leprince) appear to be impure substances.

Cascara bark yields about 27 per cent. of aqueous extract and 5 per cent. of ash. '

Uses

Cascara sagrada is tonic and stomachic in small doses, aperient in large doses, and cathartic if freely given. It is said to be more active and more certain than alder buckthorn.

Substitutes

The bark of B. califomicus, Eschscholz, is said to have been substituted for that of B. Purshianus. The shrub occurs sparingly in North California, but abundantly in the south and east of the State, as well as in Arizona, New Mexico, and Texas. The bark is said to be distinguished by its dull grey, slightly reddish cork, its fewer lenticels and uniform coat of lichens; the inner surface is said to be paler, and the medullary rays commonly 3 to 4 cells wide, those of B. Purshianus being only 2 to 3 cells wide. The two plants are, however, so closely allied that some botanists refer them to the same species.

The bark of Bhamnus catharticus, Linne, also contains frangula-emodin together with chrysophanol, rhamnosterin and a fluorescent body, rhamnofluorin.