As to the contents of the tissue of cinchona barks, crystallized alkaloids are not visible. Howard has published figures representing minute rounded aggregations of crystalline matter in the cells, which he supposes to be kinovates of the alkaloids; and also distinct acicular crystals which he holds to be of the same nature. These remarkable appearances are easily observable, yet only after sections of the bark have been boiled for a minute in weak caustic alkali and then washed with water; it may well be doubted whether they are strictly natural. The liquids which are capable of dissolving the alkaloids in the free state do not afford any if they are applied to the barks. The alkaloids being contained in the bark in the form of salts, the latter are decomposed by caustic lye, and the alkaloids set at liberty assume the crystallized state. This is in our opinion the origin of the crystals under notice.
The greater number of the parenchymatous cells are loaded with small starch granules, or in young and fresh barks with chlorophyll. In several barks, as in that of C. lancifolia Mutis, numerous cells of the middle cortical layer and even of the medullary rays, are provided with somewhat thick walls, and contain either a soft brown mass or crystalline oxalate of calcium. These cells have therefore been called resin-cells and crystal-cells; they are mostly isolated, not forming extensive groups or zones, and their walls are not strongly thickened as in true sclerenchymatous tissue. If thin sections of the barks are moistened with dilute alcoholic perchloride of iron, the walls of the cells, except the fibres and the cork, assume a blackish-green due to cincho-tannic acid; this applies even to the starch granules.
Characters of particular sorts.—The modifications of general structure just described, are sufficient to impart a special character to the bark of many species of Cinchona, provided the bark is examined at its full development, the structural peculiarities being far from well-marked in young barks.
Thus it is not possible to point out any distinctive features for the Loxa Bark of commerce, because it is mostly taken from young wood. We may say of it, that neither resin-cells nor crystal-cells occur in its middle layer, that its laticiferous vessels become soon obliterated, and have indeed disappeared in the older quills; and that the liber-fibres form interrupted, not very regular, radial rows.
The quills of C. Calisaya display large laticiferous ducts, which are wanting in the flat bark. There is a peculiar sort of the latter called Bolivian Calisaya (already mentioned at [p. 353]), the flat pieces of which still possess very obvious laticiferous vessels. As to the liber-fibres of Calisaya bark, they are, as before stated ([p. 356]), scattered throughout the parenchymatous tissue or endophlœum. In the bark of C. scrobiculata, which might at first sight be confounded with Calisaya bark, the liber-fibres form radial, less interrupted rows. The microscope affords therefore the means of distinguishing these two barks.
The barks of C. succirubra are particularly rich in laticiferous ducts, mostly of considerable diameter, in which the formation of new parenchyme may not unfrequently be observed. The orange liber-fibres occurring in this bark are less numerous, more scattered, and of smaller size than in Calisaya. The fracture of Red Bark, especially the flat sort, is therefore more finely granular and not so coarse as that of Calisaya.
The structural characters of Cinchona barks may lastly be fully appreciated by examining barks of the allied genera Buena, Cascarilla and Ladenbergia, which were formerly known under the name of False Cinchona Barks. The microscope shows that the liber-fibres of the latter are soft, branched and long, densely packed into large bundles, imparting therefore a well-marked fibrous structure. The external appearance of these barks is widely different from that of true cinchona barks; none of them it would appear is now collected for the purpose of adulteration.
Chemical Composition—The most important and at the same time peculiar principles of Cinchona bark are the Alkaloids,—enumerated in the following table:—[1352]
| Cinchonine | C₂₀H₂₄N₂O. |
| or, as proposed by Skraup (1878) | C₁₉H₂₂N₂O. |
| Cinchonidine (Quinidine of many writers) | same formula. |
| Quinine | C₂₀H₂₄N₂O₂. |
| Quinidine (Conquinine of Hesse) | same formula. |
| Quinamine | C₁₉H₂₄N₂O₂. |
| Conquinamine (Conchinamine) | same formula. |
B. A. Gomes[1353] of Lisbon (1810) first succeeded in obtaining active principles of cinchona, by treating an alcoholic extract of the bark with water, adding to the solution caustic potash, and crystallizing the precipitate from alcohol. The basic properties of the substance thus obtained, which Gomes called Cinchonino, were observed in the laboratory of Thénard by Houtou-Labillardière, and communicated to Pelletier and Caventou.[1354] Shortly before that time, Sertürner had asserted the existence of organic alkalis: and the French chemists, guided by that brilliant discovery, were enabled to show that the Cinchonino of Gomes belonged to the same class of substances. Pelletier and Caventou, however, speedily pointed out that it consisted of two distinct alkaloids, one of which they named Quinine, the other Cinchonine. In 1827 the Institut de France awarded to the two chemists for their discovery the Montyon prize of 10,000 francs (see page 57, note 4).