1. Pale Cinchona Bark, Loxa Bark, Crown Bark[1337]—This bark, which previous to the use of Quinine and for long afterwards, was the ordinary Peruvian Bark of English medicine, is only found in the form of quills, which are occasionally as much as a foot in length, but are more often only a few inches or are reduced to still smaller fragments. The quills are from ¾ down to an ⅛ of an inch in diameter, often double, and variously twisted and shrunken. The thinnest bark is scarcely stouter than writing paper; the thickest may be ⅒ of an inch or more.[1338] The pieces have a blackish brown or dark greyish external surface, variously blotched with silver-grey, and often beset with large and beautiful lichens. The surface of some of the quills is longitudinally wrinkled and moderately smooth; but in the majority it is distinctly marked by transverse cracks, and is rough and harsh to the touch. The inner side is closely striated and of a bright yellowish-brown.
The bark breaks easily with a fracture which exhibits very short fibres on the inner side. It has a well-marked odour sui generis, and an astringent bitter taste. Though chiefly afforded by C. officinalis, some other species occasionally contribute to furnish the Loxa Bark of commerce as shown in the conspectus at [p. 355].
2. Calisaya Bark, Yellow Cinchona Bark.[1339]—This bark, which is the most important of those commonly used in medicine, is found in flat pieces (α.), and in quills (β.), both afforded by C. Calisaya Wedd., though usually imported separated.
α. Flat Calisaya—is in irregular flat pieces, a foot or more in length by 3 to 4 inches wide, but usually smaller, and ²/₁₀ to ⁴/₁₀ of an inch in thickness; devoid of suberous layers and consisting almost solely of liber, of uniform texture, compact and ponderous. Its colour is a rusty orange-brown, with darker stains on the outer surface. The latter is roughened with shallow longitudinal depressions, sometimes called digital furrows.[1340] The inner side has a wavy, close, fibrous texture. The bark breaks transversely with a fibrous fracture; the fibres of the broken ends are very short, easily detached, and with a lens are seen to be many of them faintly yellowish and translucent.
A well-marked variety, known as Bolivian Calisaya, is distinguished for its greater thinness, closer texture, and for containing numerous laticiferous ducts which are wanting in common flat Calisaya bark.
β. Quill Calisaya—is found in tubes ¾ to 1½ inch thick, often rolled up at both edges, thus forming double quills. They are always coated with a thick, rugged, corky layer, marked with deep longitudinal and transverse cracks, the edges of which are somewhat elevated. This suberous coat, which is silvery white or greyish, is easily detached, leaving its impression on the cinnamon-brown middle layer. The inner side is dark brown and finely fibrous. The transverse fracture is fibrous but very short. The same bark also occurs in quills of very small size, and is then not distinguishable with certainty from Loxa bark.
3. Red Cinchona Bark.—Though still retaining a place in the British Pharmacopœia, this is by far the least important of the Cinchona barks employed in pharmacy. But as the tree yielding it (C. succirubra) is now being cultivated on a large scale in India, the bark may probably come more freely into use.
Red Bark of large stems, which is the most esteemed kind, occurs in the form of flat or channelled pieces, sometimes as much as ½ an inch in thickness, coated with their suberous envelope which is rugged and warty. Its outermost layer in the young bark has a silvery appearance. The inner surface is close and fibrous and of a brick-red hue. The bark breaks with a short fibrous fracture.[1341]
(C.) Of the Barks not used in pharmacy—Among the non-officinal barks, the most important are afforded by Cinchona lancifolia Mutis and C. pitayensis Wedd., natives of the Cordilleras of Columbia.
These barks are largely imported and used for making quinine, the former under the name of Columbian, Carthagena, or Caqueta bark. It varies much in appearance, but is generally of an orange-brown; the corky coat, which scales off easily, is shining and whitish. The barks of C. lancifolia often occur in fine large quills or thick flattish pieces. Their anatomical structure agrees in all varieties which we have examined, in the remarkable number of thick-walled and tangentially-extended cells of the middle cortical layer and the medullary rays. In percentage of alkaloids, Carthagena barks are liable to great variation.