156 SCIENTIFIC AND APPLIED PHARMACOGNOSY 



Description. In quills or in long flat pieces, sometimes as long as 

 1 M. and from 0.5 to 1 mm. in thickness; outer surface yellowish- 

 brown or blackish-brown, irregularly wrinkled and rough-scaly in the 

 older bark; inner surface cinnamon brown, finely longitudinally 

 wrinkled ; fracture short fibrous, the inner portion separable into thin 

 layers; the cut surface colored red with sulphuric acid (presence of 

 salicin), and colored dark green upon the addition of a solution of a 

 ferric salt (presence of tannin); odor slight, aromatic; taste bitter 

 and astringent. 



Inner Structure. The epidermal cells when present possess thick, 

 nearly uniform outer walls. The cork cells are developed within the 

 hypodermis and are much thickened on the outer walls. The primary 

 bark consists of a layer of small collenchymatous cells and paren- 

 chyma containing starch, rosettes of calcium oxalate, tannic acid and 

 sometimes chloroplastids. The inner bark consists of small groups 

 of bast fibers and leptome separated by 1-celled medullary rays; the 

 groups of bast fibers are surrounded by crystal fibers, each containing 

 a rhombohedral crystal of calcium oxalate. 



Constituents. A bitter glucoside, Salicin, the amount of which 

 varies in different portions of the bark and according to the time when 

 it is gathered, as follows: outer bark, 2.5 per cent; middle bark, 5.8 

 per cent; innermost layers, 11.3 per cent; bark collected in spring, 

 7.38 per cent; and that gathered in the fall, 6.66 per cent. Salicin 

 through the actions of ferments forms saligenin, which latter when 

 taken into the human system is decomposed into salicylic acid. The 

 drug also contains 13 per cent of tannic acid; calcium oxalate, gum 

 and wax. 



Salicin crystallizes in orthorhombic prisms and when examined 

 by means of polarized light, using crossed Nicols, they display beau- 

 tiful colors. For color plate showing these crystals in polarized 

 light, consult Kraemer's Applied and Economic Botany. 



Allied Plants. The bark of the black willow (Salix nigra) is used 

 to some extent in this country. The tree is rather common in the 

 United States, growing almost everywhere excepting California. The 

 bark of Salix discolor contains, in addition to salicin, the glucoside of 

 metahydroxybenzaldehyde, salinigrin. Power, Pharm. Jour., 1902 

 (69), p. 157. 



Literature. Zornig, Arzneidrogen. 



CARBO LIGNI. Carbo Ligni Pulveratus, Carbo Ligiri Depura- 

 tus, or Wood Charcoal. The carbonaceous residue that remains 

 after heating, without access of air, the wood of one of more species 

 of the following genera: Salix, Populus, Quercus or Corylus. 



