254 



BARKS 



The transverse section is seen under a lens to be traversed by parallel 

 tangential and radial lines, which give it a chequered appearance ; the 

 tangential lines are tangentially arranged bands of bast parenchyma, 

 the radial are medullary rays, the darker portions between being 

 groups of bast fibres. 



The bark is almost odourless, but the powder is extremely irritating 

 to the nostrils and fauces and gives rise to prolonged fits of sneezing ; 



the taste is acrid and unpleasant. 

 The student should observe 



(a) The splintery, laminated frac- 



ture, 



(b) The glittering crystals of calcium 



oxalate, 



(c) The very smooth inner surface, 

 (b) The appearance of the transverse 



section ; 



and should compare this bark with 



(i) Elm bark, which is fibrous and 

 has a roughish, not smooth, 

 inner surface, 



(ii) Slippery elm bark, which has a 

 decided odour of fenugreek 

 and is very fibrous. 



Constituents. The principal con- 

 stituents of quillaja bark are two 

 colourless, amorphous, toxic glucosides, 

 quillajic acid and quillajasapotoxin. 



FIG. 129.-Quillaja bark, show- Both of these substances impart to 

 ing splintery fracture. Nat- water the property of frothing, and 

 uralsize. possess other characters common to 



the class of substances known as 



' saponins ' (see below). The drug also contains sucrose. 



The saponins are nitrogen -free glucosides of acid or neutral reaction ; most 

 of them are soluble in water and in hot dilute alcohol, less soluble in strong 

 alcohol, insoluble in ether, and all of them are capable of imparting to water 

 the property of frothing freely like soap solution. They are widely distributed, 

 having been found in 200 plants belonging to 50 natural orders, but are most 

 strongly represented in the orders Caryophyllacece and Sapindacece. They are 

 all glucosidal, and yield by hydrolysis a non- toxic sapogenin together with 

 sugar, a pentose and a hexose being often simultaneously produced. 



All saponins are toxic when introduced directly into the circulation, but the 

 degree of toxicity varies greatly ; they are protoplasmic poisons, irritating and 

 killing protoplasm and dissolving red blood-corpuscles. Taken by the mouth 

 some can be borne in considerable quantity. Almost all of them stupefy fish 



