282 BARKS 



The bark has a strong odour resembling fenugreek, and a very 

 mucilaginous taste. 



The student should observe 



(a) The striated inner and outer surface, 



i b) The fibrous fracture, 



(c) The odour of fenugreek and the mucilaginous taste ; 



and should compare the bark with 



Quillaja bark, which has a splintery fracture, a smooth 

 inner surface, and is odourless. 



Constituents. The principal constituent is mucilage, which ap- 

 pears to swell but not dissolve in water ; it is contained in large 

 mucilage cells in the bast, and is present in such proportions that 1 gm. 

 of the powdered bark will convert 50 c.c. of water into a thick jelly. 



Uses. The bark has demulcent and emollient properties. It is 

 chiefly used as an external application in the form of a poultice. 



OAK BARK 



(Cortex Quercus) 



Source, &c. The British oak, Quercus robur, Linne (N.O. Cupu- 

 liferce), is widely diffused over Europe and largely cultivated for 

 its wood and especially for its bark, which, from the large proportion 

 of tannin it contains, is valued highly for tanning. Although the 

 astringent properties of the bark have long been known, and although 

 it has been used from time immemorial in preparing leather, it never 

 appears to have been much used in medicine. 



In the collection of oak bark the trees are usually felled when they 

 have reached an age of twelve to thirty-five years, and in the early 

 spring when the buds are opening. Longitudinal incisions are made 

 through the bark, which can then be removed in strips, and after 

 drying is ready for the market. 



Young bark is preferable to old, because as the trees increase in 

 age the outer portions are cut off by the production of layers of cork 

 in the bast (formation of outer bark), and the tannin in the portions 

 thus cut off undergoes certain changes. Bark from older stems is 

 also collected and freed from its dead outer portions, but such bark 

 is not so valuable for tanning or fit for medicinal use. 



From the stools that are formed when the trees are felled adven- 

 titious shoots arise, and these, when they have attained a sufficient 

 age, are cut and peeled. 



While the bark is young (up to about twenty years old) it 



