Source, Etc

Quillaja bark, or, as it is often called, soap bark, is obtained from Quillaja saponaria, Molina (N.O. Bosaceoe), a large tree indigenous to Chili and Peru. The bark, which is called 'cullay' by the natives and has apparently been long used by them for washing silk and wool, was known to Europeans in the early part of the eighteenth century, but was not regularly imported until about 1857, when it was sent to France under the name of 'Bois de Panama,' the name indicating the route by which it was sent. It is evidently stripped from the trees, freed from the outer dark brownish portion (bark), and dried. The tree has been introduced into India, where it yields a bark identical with the commercial drug.

Description

Soap bark comes into commerce in large flat pieces about a metre in length and 10 or 15 cm. in breadth; it is usually about 6 mm. thick, and evidently the produce of trunks of considerable size.

The outer surface is usually of a pale brownish or yellowish white colour longitudinally striated and streaked with reddish brown where the outer portion (bark) has been imperfectly removed. Sometimes, from insufficient trimming, the bark is of a uniform dark dull red colour and bears patches of the outer bark still adhering to it. The inner surface is smooth and white or yellowish white.

The bark breaks with a splintery fracture, and the fractured surface exhibits a disposition to separate into thin plates or laminae. Here and there, especially on the freshly fractured laminated surfaces, but also on the smooth inner surface of the bark, minute, glittering, prismatic crystals (calcium oxalate) can be seen with the naked eye, or better with a lens; sometimes these are present in considerable numbers.

The transverse section is seen under a lens to be traversed by parallel tangential and radial lines, which give it a chequered appearance; the tangential lines are tangentially arranged bands of bast parenchyma, the radial are medullary rays, the darker portions between being groups of bast fibres.

The bark is almost odourless, but the powder is extremely irritating to the nostrils and fauces and gives rise to prolonged fits of sneezing; the taste is acrid and unpleasant. The student should observe

(a) The splintery, laminated fracture,

(b) The glittering crystals of calcium oxalate,

(c) The very smooth inner surface, (b) The appearance of the transverse section; and should compare this bark with

(i) Elm bark, which is fibrous and has a roughish, not smooth, inner surface,

(ii) Slippery elm bark, which has a decided odour of fenugreek and is very fibrous.

Constituents

The principal constituents of quillaja bark are two colourless, amorphous, toxic glucosides, quillajic acid and quillajasapotoxin. Both of these substances impart to water the property of frothing, and possess other characters common to the class of substances known as 'saponins' (see below). The drug also contains sucrose.

Fig. 129.   Quillaja bark, showing splintery fracture. Natural size.

Fig. 129. - Quillaja bark, showing splintery fracture. Natural size.

The saponins are nitrogen-free glucosides of acid or neutral reaction; most of them are soluble in water and in hot dilute alcohol, less soluble in strong alcohol, insoluble in ether, and all of them are capable of imparting to water the property of frothing freely like soap solution. They are widely distributed, having been found in 200 plants belonging to 50 natural orders, but are most strongly represented in the orders Caryophyllaceoe and Sapindaceoe. They are all glucosidal, and yield by hydrolysis a non-toxic sapogenin together with sugar, a pentose and a hexose being often simultaneously produced.

All saponins are toxic when introduced directly into the circulation, but the degree of toxicity varies greatly; they are protoplasmic poisons, irritating and killing protoplasm and dissolving red blood-corpuscles. Taken by the mouth some can be borne in considerable quantity. Almost all of them stupefy fish even when present in small proportion (1: 200,000) only. With concentrated sulphuric acid they produce a characteristic red coloration; with a mixture of alcohol and sulphuric acid and ferric chloride a green colour is obtained.

The saponins have been classified in two series, viz. acid saponins (quillajic acid, polygalic acid, guaiacsaponic acid, etc.) and neutral saponins (quillaja-sapotoxin, senegin, parillin, guaiacsaponin, &c). The composition of many of them may be expressed by the general formula CnH1n_8O10 (Kobert); for neutral saponins of the formula C17H16O10 the name of sapotoxin is reserved.

Commercial saponin is usually obtained from quillaja bark, and is a mixture of quillajic acid, quillaja-sapotoxin, and frequently also a non-toxic modification of quillajic acid produced during the preparation; as the term saponin has become a generic one, a prefix to indicate the source would be desirable.

Quillajic acid, C19H30O10, has been obtained as a colourless amorphous mass, the powder of which is strongly sternutatory. The aqueous solution is acid and has an acrid taste. Boiled with a mineral acid it yields quillaja-sapogenin, galactose, and another sugar, which is non-fermentable and dextrorotatory.

Quillaja-sapotoxin, C17H16O10, is also white, amorphous, sternutatory, and acrid.

Uses

Quillaja bark has been recommended as a stimulant and expectorant, but has not met with much favour. A tincture is largely used as a means of emulsifying tars, etc.

Substitutes

A quillaja bark differing from the foregoing in being thinner and in having a more or uniform, distinctly reticulated outer layer has been imported; its botanical origin is unknown (possibly Q. Poeppigii, Walp.). Another variety in quills 7 to 15 cm. long, 1 to 2.5 cm. wide and about 3 mm. thick, softer and not laminated, has been referred to Q. smegmadermos, de Candolle.