GUAIACUM 225 



straight, and closely approximated ; the vessels are distinct, usually 

 single, and arranged in concentric zones. 



The wood splits very irregularly, owing to the oblique and varying 

 course taken by the wood fibres. Both these and the vessels in 

 fact, all the elements of the heartwood are filled with a dark resin, 

 which is sometimes also found in cavities in the trunk. It exhales, 

 when warmed, a faint aromatic odour, recalling benzoin, and has, 

 when chewed, an acrid taste. Its toughness and hardness render 

 it valuable for many technical purposes, it being used in making 

 blocks, pulleys, &c. The chips or turnings, in which state it is usually 

 employed in pharmacy, should consist of the dark-coloured heart 

 wood alone, but they are frequently mixed with the pale yellow 

 sapwood from which they may be separated by a 30 per cent, solution 

 of sodium chloride in which the splinters of heartwood sink. The 

 sapwood contains about 3 per cent, of resin, not identical with the 

 resin of the heartwood. 



The student should observe 



(a) The pale colour of the sapwood, 



(b) The dark greenish brown heartwood, 



(c) The distribution of the vessels. 



Microscopical Characters. The vessels are large and isolated, often extending 

 from one medullary ray to the next. The medullary rays are one cell wide and 

 three to six cells high. The wood-fibres are abundant and have very thick 

 walls. The wood parenchyma occurs in narrow bands and some of the cells 

 contain prismatic crystals of calcium oxalate. 



Constituents. The heartwood of guaiacum contains between 20 

 and 25 per cent, of resin, which has been found to consist of a- and 

 /3-guaiaconic acids, guaiaretic acid, and guaiacic acid. Guaiaconic 

 acid is converted by oxidising agents into guaiac blue and accor- 

 dingly tincture of guaiacum wood strikes a deep blue colour with 

 dilute solution of ferric chloride, a reaction which is useful in 

 identifying the wood. (Compare ' Guaiacum Resin.') 



Guaiacum wood also contains guaiacsaponic acid and guaiac 

 saponin, two non-toxic bodies belonging to the class of saponins ; 

 they are present in larger quantity in the sapwood than hi the heart- 

 wood. Guaiaguttin, which resembles gutta-percha, is also present. 



Guaiaconic acid, though a characteristic constituent of the wood, 

 has been found in other woods (e.g. species of Bulnesia and Porlieria), 

 and its presence therefore is not an Infallible diagnostic character 

 of guaiacum wood. 



Uses. Guaiacum has a local stimulant action which is sometimes 

 useful in sore throat. The resin is used in chronic gout and rheu- 

 matism, whilst the wood is an ingredient in the compound concen- 

 trated solution of sarsaparilla, which is used as an alterative in 

 syphilis. 



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