Cinchona bark occasionally varies in its powers, and is often mixed with other inferior barks, even by the bark peelers (cascarilleros) who gather it. This arises either from ignorance, or from a fraudulent desire of more quickly completing their contracts5; it is, therefore, of importance to be able to distinguish good bark, and the best varieties from those of an inferior description. Mutis informs us, that the old trees furnish the best bark; and that the bark taken from the trunk and thicker branches is superior to that from the younger branches. The following directions for choosing bark are those generally attended to in South America 6 : -The essential characteristics are colour, taste, and smell: the secondary, or accidental ones, are exterior coat, fracture, weight, thickness, and quill. The best yellow bark is of an orange-yellow colour; and the goodness decreases as the colour varies from this to a very pale yellow. When of a dark colour, between red and yellow, it is always to be rejected; as this colour designates either that it is of a bad species, or that it has not been well preserved from the air and moisture. This dark colour, however, must not be confounded with a red colour in the inside, which constitutes a distinct species.

The taste of bark should be bitter, but not nauseous nor very astringent, with a slight agreeable acidity just perceptible to the palate; and, when chewed, it should not appear in threads of much length. The odour of any of the barks is not very strong : but, when they have been well cured and preserved, it is always perceptible; and the stronger it is, provided it be pleasant, the better may the bark be considered. The appearance of the coat or epidermis has led to mistakes. It is, in many instances, merely accidental; depending on the variation in the height of the ground, and the exposure of the branches to the sun and air. Seven distinct appearances of the epidermis are remarked; 1. Negrilla, Dark silver coat1; 2. Crespilla, short curled; 3. Pardo-obscura, dark open leopard grey2; 4. Pardo-clara, light open grey3; 5. Lagartijada, fine dark silver, lizard-coloured4; 6. Blanquissima, very pale5; and, 7. Cenicienta, ash-coloured. The first three are the best, and belong to bark produced on the highest mountains; the others rank in the order of their arrangement; the epidermis being always cracked and rough in proportion as the trees have been exposed to a scorching sun.

With regard to fracture, some of the worst barks break even and clean as if cut with a knife, and some of the best have always a more or less splintery fracture.6 The fibres of the fracture being sharp and short, indicate the bark to have been gathered from mature branches; the long and thread-like from immature branches. The best barks are generally observed to be the heaviest. In point of thickness, very thin bark is inert, owing to the branches from which it was taken having been too young; and very thick bark, particularly if it break like common wood, argues that the tree must have been sickly; yet bark exceeding a line in thickness may be good: for although it is disapproved of at Cadiz, under the name of quinon, yet excellent effects have resulted from much thicker bark in England. The moderately thick and firm bark is always preferred at Lima. The quilling of bark arises from the manner in which it is separated from the branches. This is effected by making a longitudinal incision in the branch, and passing under the bark a very fine knife.

As the slip dries, it rolls up, owing to the internal surface shrinking more than the external: a feeble rolling, therefore, denotes that the bark is rather too old, or has been too slowly dried; too much quilling, that it is either too young, or has been too hastily dried. The moderate quill of bark certainly denotes it to be of the best kind, and that it has been taken from branches of a proper age, and well dried; but the bark-collectors often produce this effect by fire, when there is a want of sun, as is frequently the case in some parts of the mountains. The fraud is known by the colour being much darker; and, when the bark is split, the inside exhibiting stripes of a whitish sickly hue. It should be preserved in cases, well secured from the air and humidity.

1 Geiger. 2 Sieberg.

3 The Carthagena barks; namely, C. cordifolia of Mutis, C. oblongifolia, brown Cat thagena bark, and the bark of Santa Martha, contain less of the alkaloids than the Peruvian barks.

4 Memoir on Quinquina, by M. Laubert, Chief Physician to the Spanish Army: translated in Lambert's Illustrations, 4to. 1821, p. 64.

5 Humboldt says, "We saw at Peru the barks of two new species of Wein-mannia and Wintera mixed with those of Cinchona." Pei-sonal Narrative, vol. v. p. 769. Trans.

6 Extracted from a MS. of Don Felix Devoti, a respectable physician at Lima, who had practised upwards of twenty-five years in South America.

1 This bark is occasionally found amongst the pale cinchona sent to England. It is easily distinguished by its spotted surface. Ruiz says it must be ranked among those of a middling quality.

2 This is found mixed with the pale bark of the shops. It is regarded as of middling quality.

3 This is a very rare bark, and is that of the C. fusca of Ruiz. It is called Asmonich by the natives of Puzuzu and Muna, where it is found.

4 The bark with this coat has the greatest affinity with the yellow bark of the shops. It is a good kind of bark.

5 This bark is little valued in Spain, and is seldom met with in commerce. 6 The idea of a resinous fracture being the characteristic of good bark originated when the virtue of bark was supposed to depend on the resin it contained. .

Analytical examinations of cinchona. -These have been made with the view of discovering on what principle its febrifuge properties depend, and chymists well qualified for the task have engaged in it. In giving a short history of their trials, we need not go further back than Vauquelin : he divided all the different species into three sections, according to their chymical properties.1 The first comprised those which precipitate tannin, but not animal gelatine; the second, those which precipitate gelatine, but not tannin; and the third, those which precipitate at the same time tannin, gelatine, and tartar emetic. He conjectured, that on the principles producing these effects, particularly that which precipitates infusion of galls, the febrifuge properties of the barks depend, and that they are more or less febrifuge, in proportion to the quantity of these principles that are present. He asserted that the principle which precipitates tannin is of a brown colour and bitter taste; is less soluble in water than in alcohol; and that it also precipitates tartarized antimony, but not glue.2 He imagined that it possessed some analogies with the resinous bodies, although it furnished ammonia on distillation; whilst the principle which, in some cinchonas, precipitates glue, has a bitter and astringent taste; is more soluble in water than the principle which, in other kinds, precipitates tan: it is also soluble in alcohol, and does not precipitate tartar emetic.1 Reuss of Moscow, along with a red matter, which he named cinchonic red, procured a bitter principle, probably Quina; but its nature was not ascertained.