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       Himalayan Birch Bark is the dried stem bark of Betula alnoides Buch.-Ham. ex D. Don [B. affinis (Spach) Endl., B. nitida D. Don] (Family Betulaceae), Herbarium Specimen Number: DMSC 5332, Crude Drug Number: DMSc 1226.

Constituents Himalayan Birch Bark contains triterpenoids (e.g., betulin, betulinic acid, lupeol, oleanolic acid, and ursolic acid). It also contains phenolics such as methyl salicylate and arbutin.

Description of the plant (Fig. 1) Tree up to 35 m tall, monoecious; bark red-brown or silvery grey, with large oblong lenticels, exfoliating into thin slices; inner bark strongly aromatic; branchlet densely white villous, with resinous glands. Leaves simple, spirally arranged, ovate-lanceolate, ovate-elliptic, to ovate-oblong, 4 to 14 cm long, 2.5 to 5.5 cm wide, apex acuminate or caudate-acuminate, base cuneate to broadly cuneate or subrounded, rarely subcordate, margin serrate, papery, abaxially densely glandular punctate, sparsely villous along veins, bearded in axils of lateral veins, adaxially glabrous, lateral veins 8 to 13 on each side of midvein; petiole 1.5 to 4 cm long, densely white villous, with resinous glands. Inflorescence terminal or axillary pendulous catkins, cylindrical; pedunculate. Flower tiny, greenish, perianth minute. Staminate inflorescence up to 20 cm long, about 4 mm wide; bracts numerous, overlapping, each bract subtending 2 bracteoles and 3 flowers; staminate flowers: stamens 2, anthers 2-loculed, thecae connate, apex pubescent or glabrous. Pistillate inflorescence 5 to 10 cm long, 4 to 6 mm wide, in group of 2 to 5; peduncle 2 to 3 mm long, densely yellow villous; bract about 3 mm long, densely pubescent and ciliolate, becoming spongy at base, 3-lobed, middle lobe oblong or obtuse, lateral lobes reduced, auriculate, each bract subtending 3 ovaries at base; pistillate flowers: ovary, 2-loculed, each locule with 2 ovules, styles 2, persistent. Fruit a nutlet, with membranous wings; nutlet obovate, about 4 mm long (wings included), apex sparsely pubescent, flattened, with membranous wings twice as wide as nutlet.

Description Odour, slightly methyl salicylate-like; taste, slightly pungent.

Macroscopical (Fig. 1) Curved stem bark, 1.0 to 3.5 cm thick. Outer surface whitish brown to reddish brown, slightly rough, with parts of exfoliated yellowish brown of remained periderm, phellem slightly with scattered long horizontal whitish shallow groove of lenticels. Inner surface smooth, reddish brown.

Microscopical (Figs. 2a, 2b) Transverse section of the stem bark shows outer bark and inner bark. Outer bark: several layers of cork, some containing brown or red substance and groups of sclereids, some containing brown or red substance. Inner bark: groups of sclereids, phloem ray, phloem fibres, and phloem parenchyma, some containing starch grains, prismatic crystals, rosette aggregate crystals or brown substance.

Himalayan Birch Bark in powder possesses the diagnostic microscopical character of the unground drug. Groups of thick-walled sclereids with brown or red substance and thick-walled parenchyma containing brown substance are characteristic.

Packaging and storage Himalayan Birch Bark shall be kept in well-closed containers, protected from light, and stored in a cool and dry place.

Identification

       A. To 1 g of the sample, in No. 250 powder, add 30 mL of water and heat on a water-bath for 20 minutes. Immediately filter through a plug of cotton wool and allow the filtrate to cool. Shake 5 mL of the filtrate with 2 mL of chloroform for 2 minutes. Separate the chloroform layer and transfer 1 mL of this layer to a test-tube, slowly add a few drops of sulfuric acid to form a layer: a reddish brown ring forms at the zone of contact.
       B. Boil 1 g of the sample, in No. 250 powder, with 20 mL of water, cool and filter. To 1 mL of the filtrate, add 5 mL of water, mix and then add a few drops of iron(III) chloride TS: a dark blue precipitate develops.
       C. Carry out the test as described in the “Thin-Layer Chromatography” (Appendix 3.1), using silica gel GF254 as the coating substance and chloroform as the mobile phase and allowing the solvent front to ascend 8 cm above the line of application. Apply separately to the plate as bands of 5 mm, 4 µL each of solutions A and B. Prepare solution (A) by refluxing 2 g of the sample, in No. 250 powder, with 30 mL of ethyl acetate for 15 minutes and filtering. Evaporate the filtrate to dryness, dissolve the residue in 2 mL of methanol. For solution (B), dissolve 1 mg of lupeol in 1 mL of methanol. After removal of the plate, allow it to dry in air. Spray the plate with anisaldehyde TS and heat at 105° for 5 minutes and examine under daylight; the band corresponding to lupeol is purple (hRf value 62 to 67). Nine purple bands are also observed. Subsequently examine the same plate under ultraviolet light (366 nm); the band due to lupeol shows purple fluorescence; two yellow and seven blue fluorescent bands are also observed (Fig. 3).

Loss on drying Not more than 9.0 per cent w/w after drying at 105° to constant weight (Appendix 4.15).

Foreign matter Not more than 2.0 per cent w/w (Appendix 7.2).

Total ash Not more than 3.0 per cent w/w (Appendix 7.7).

Ethanol-soluble extractive Not less than 12.0 per cent w/w (Appendix 7.12).

Water-soluble extractive Not less than 8.0 per cent w/w (Appendix 7.12).