594 CUPULIFER^. 



History— The astringent properties of all parts of the oak^ were 

 well known to Discorides, who recommends a decoction of the inner 

 hark in colic, dysentery and spitting of blood. Yet oak bark seems at 

 no time to have been held in great esteem as a medicine, probably on 

 account of its commonness; and it is now almost superseded by other 

 astringents. For tanning leather it has ahvays been largely employed. 



Description For medicinal use the bark of the younger stems or 



branches is collected in the early spring. It varies somewhat in appear- 

 ance according to the age of the wood from which it has been taken: 

 that usually supplied to English druggists is in channelled pieces of 

 variable length and a tenth of an inch or less in thickness, smooth, of a 

 shinino- silvery grey, variegated with brown, dotted over with little scam 

 The inner surface is light rusty-brown, longitudinally striated. The 

 fracture is tough and fibrous. A transverse section shows a thin, greenish 

 cork-layer, within which is the brown parenchy me, marked with nume- 

 rous rows of translucent colourless spots. The smell of dry oak bark is 



moistened 



evident. The taste 

 Microscooic S 



;— The outer layer of young oak bark con- 



cells slightly extended in a tangential direction, and containing brown 

 grains and chlorophyll. This tissue passes gradually into the sotter 

 narrower parenchyme of the inner bark, which is irregularly traversed 

 by narrow medullary rays. It exhibits moreover a ring, but slightly 

 interrupted, of thick-walled cells (sclerenchyme) and isolated shining 

 bundles of liber fibres. , 



Groups of crystals of calcium oxalate are frequent in the middle ana 

 inner bark, but the chief constituents of the cells are brown granules oi 

 colouring matter and tannin. As the thickness of the bark increases 

 the liber is pushed more to the outside, the middle cortical layer bein^ 

 partly thrown off by secondary cork-formation (rhytidoma, see pp. 

 and 538). Hence the younger barks, which alone a,re medicinal, are 

 widely different from the older in structure and appearance. 



The most interesting constituent is a 



mical Com 



peculiar kind of tannin. Stenhouse pointed out in 1843 taa 

 tannic acid of oak bark is not identical with that of nutgalls; ana su 



Querci 



by destructive distillation pyrocatcchin, and according ^^/^l jj 

 (1875) very little pyrogallol. By boiling it with dilute sulphunc ^ 

 querci-tannic acid is split up into a red derivative and sug • 



arelatine 



ereas 



panied by a large amount of extractive matter, furnishes a sta 



formin 



state, the 



exact 



As querci-tannic acid has not yet been isolated in a pure :^^^ 

 ct estimation of the strength of the tanning principle m o^^ ■ 



gm OI ^ne^Lanning p ...n- ^^^^,^,c 



1 



c point of view. T 



Probably not Q. Rohur L. 



Neubai^^^ 



