The colour of the inner surface is usually yellowish brown, and the taste resembles that of calisaya bark in being bitter as well as astringent. 4. G. succirubra. - This species yields a drug that is characterised by a more or less distinct reddish colour, and is therefore usually known as ' red bark '; it occurs in two forms, viz. 'flat' and 'quill.'

The former is occasionally imported from South America; the latter is obtained from cultivated trees, and is imported principally from Java.

(a) Flat red bark occurs in flattish pieces, often of considerable size, and attaining 20 mm. in thickness, though usually thinner; in these respects it resembles flat calisaya, but it differs from that bark essentially in having the outer bark attached; the latter is rugged, of a dusky, ferruginous red colour, and marked with longitudinal ridges of cork as well as brighter red warts. The inner surface has also a distinctly red colour, and does not exhibit the wavy fibrous structure characteristic of flat calisaya.

The bark has a bitter and markedly astringent taste.

(B) Quill Red Bark

The only official cinchona bark is that obtained from the stem and branches of cultivated plants of C. succirubra. The quills vary in size, but are often about 25 mm. in diameter. The outer surface is of a dull brownish grey or reddish brown colour, and often bears numerous greyish lichens attached to it. It is always more or less strongly wrinkled longitudinally, and marked with warts which are sometimes small and numerous or sometimes larger and scattered; in the latter case they are usually either reddish in colour or exhibit a reddish colour when broken. Some varieties of the bark bear small transverse cracks and reddish warts, the longitudinal wrinkles being less pronounced. In thickness the bark varies from 2 to 4 mm. The colour of the inner surface is in typical specimens reddish brown, but that of the interior of the bark is yellowish brown. This colour is due to a change in the tannin of the bark, by which a reddish phlobaphene is produced. The bark has a distinctly astringent and bitter taste. The Pharmacopoeia requires that it shall yield between 5 and 6 per cent, of total alkaloid, of which not less than half should consist of quinine and cinchonidine.

Branch bark may generally be distinguished from trunk bark by being thinner, by bearing more numerous wrinkles and small warts, and by being more strongly inrolled.

Fig. 133.   Pale bark (G. officinalis), showing very numerous longitudinal and transverse cracks. Large specimen, natural size.

Fig. 133. - Pale bark (G. officinalis), showing very numerous longitudinal and transverse cracks. Large specimen, natural size.

Both varieties are characterised by their taste, which is more markedly astringent than that of pale or yellow bark.

5. C. lancifolia. - The cinchona barks yielded by C. lancifolia (Columbian, Cartagena barks) occur both in single quills and in flattish pieces; they are usually more or less spongy in texture and reddish brown in colour. They are characterised and easily distinguished by the presence of smaller or larger patches of silvery cork which are to be found on almost every piece. The bark has an astringent bitterish taste.

B Quill Red Bark 206Fig. 134.   Red Cinchona bark, showing longitudinal wrinkles (A), reddish warts and small transverse cracks (B). Slightly reduced.

Fig. 134. - Red Cinchona bark, showing longitudinal wrinkles (A), reddish warts and small transverse cracks (B). Slightly reduced.

Microscopical Characters

The transverse section of quilled red cinchona of moderate thickness exhibits an abundant cork layer, a cortex containing small starch grains, cells filled with sandy crystals of calcium oxalate, and, on its inner margin, large isolated oval laticiferous cells. The secondary bast contains large, striated bast fibres either singly or in small radially elongated groups; these bast fibres are spindle-shaped and have conspicuous more or less funnel-shaped pits. The walls of all the parenchymatous cells are dark reddish brown in colour.

The student should carefully compare the principal varieties of cinchona bark and note the following prominent characters: 1. Quilled barks:

(a) C. succirubra; longitudinal wrinkles and reddish warts; a more or less spongy bark.

(b) C. Calisaya; longitudinal furrows, transverse cracks, cork often exfoliating; a firm hard bark.

(c) C. officinalis; very numerous small transverse and longitudinal cracks; quills usually very small and rough to the touch; a firm bark.

(d) C. lancifolia; more or less uniformly smooth surface with patches of silvery-grey cork.

FIG. 135.   Bark of Cinchona lancifolia, showing patches of silvery cork. Natural size.

FIG. 135. - Bark of Cinchona lancifolia, showing patches of silvery cork. Natural size.

(e) C. Ledgeriana; cracks more numerous than in G. Calisaya; bark rougher.

2. Flat barks:

(a) C. succirubra; ferruginous red colour, reddish warts, and raised ridges; usually in thick pieces.

(b) C. lancifolia; exhibits the characteristic silvery cork.

(c) C. Calisaya; thick pieces with a wavy fibrous surface exhibiting depressions.

Constituents

The chief constituents of cinchona barks are the alkaloids they contain, of which a number have been isolated. Some of these are well-defined crystalline substances; some have been obtained only in an amorphous condition; of others it is questionable whether they are not produced from other pre-existing alkaloids during the process of isolation.

The principal alkaloids in cinchona are quinine, cinchonidine, cinchonine, and quinidine; next in importance are hydroquinine, hydrocinchonidine, quinamine, and homocinchonidine. (For a complete list see Henry, ' Plant Alkaloids,' 1913, p. 130).

In addition to the alkaloids, many cinchona barks also contain a very bitter amorphous glucoside, quinovin; a crystalline organic acid, quinic or kinic acid, also found in coffee, in the whortleberry (Vaccinium Myrtillus, Linne), and other plants; a particular tannin, cinchotannic acid, which by oxidation rapidly yields a dark-coloured phlobaphene, cinchona red; starch, calcium oxalate, etc.

The amount of total alkaloid present in cinchona barks is subject to great variation. Quilled red bark from India averages about 6.5 per cent.; that from Java is richer, yielding about 8.25 per cent. Calisaya quills afford about 6 or 7 per cent, and pale bark about 6 per cent. Ledger bark from Java is the richest of all, yielding from 5 to 10 or even more per cent, of total alkaloid. Root-bark is the richest, and stem-bark is better than branch-bark. The relative value of a bark is, however, determined by the proportion of quinine it contains.

Quinine was first isolated by Pelletier and Caventou in 1820, after Gomez in 1811 had produced from cinchona a crystalline combination of quinine and cinchonine. It occurs in the largest proportion in Ledger bark, the highest recorded yield being 14.5 per cent. This, however, is quite exceptional, the quinine in commercial Ledger bark averaging from 3.0 to 8.0 per cent. Bolivian cultivated calisaya contains from 3'0 to 4.0, and cultivated G. officinalis about 3.0 per cent. Indian red bark contains about 1.5 per cent. of quinine, but that from Java is richer, attaining as much as 5 per cent.

Cinchonine is found in small quantity in most of the cinchona barks, especially G. lancifolia and some specimens of C. succirubra, this alkaloid is frequently more abundant in the root-bark than in the stem-bark.

Quinidine, discovered by Henry and Delondre in 1833, seldom exceeds 0.5 per cent, in any bark; it occurs chiefly in certain varieties of G. Calisaya.

Cinchonidine, isolated in 1847 by Winckler, is found more generally distributed and in much larger proportion than quinidine. The cultivated C. succirubra at present exported from India contains as a rule more cinchonidine than quinine, from 3 to 4 per cent, being frequently present.

All these alkaloids exist, according to de Vrij, combined with cinchotannic acid in the parenchymatous tissue of the bark.

Uses

The cinchona barks are far too bulky for use as antiperiodics and antipyretics if quinine can be obtained. They are therefore given only as bitter stomachics and tonics. The amount of tannin contained in them indicates that they may be used when an astringent effect also is desired.

Allied Drugs

Cuprea Bark; the bark of Remijia pedunculated, Triana, and R. purdieana, Triana (N.O. Rubiaceoe, Columbia); coppery red, dense, very hard and breaks with a short granular fracture; contains quinine, cupreine, quinidine, cinchonine, and cinchonamine; not now in commerce.

Various species of Cascarilla, Exostemma and Stenostoma; these barks contain none of the cinchona alkaloids.