248 BARKS 



and should compare the bark with 



Alder Buckthorn bark, which has deep crimson inner cork 

 layers and no sclerenchymatous cells. 



Constituents. Our knowledge of the constituents of cascara sagrada 

 is very deficient. The presence of emodin and an allied substance, 

 possibly frangula-emodin, has been definitely proved, but the latest 

 research (Jowett, 1904) failed to afford any evidence of chrysophanic 

 acid, chrysarobin, or any glucoside yielding by hydrolysis emodin, 

 chrysophanic acid, or rhamnetin. The total amount of emodin and 

 frangula-emodin (1*4 to 2'0 per cent.) present in the bark either 

 normally or after boiling with dilute sulphuric acid is quite insufficient 

 to account for the purgative action of the drug, and the real laxative 

 principle remains therefore still unknown. 



The presence of emodins may be demonstrated by the test given 

 under Alder Buckthorn bark ; the ammonia acquires a yellowish 

 red colour. 



The bitter taste of the bark appears to be due to a lactone which 

 is converted into less bitter salts by treatment with alkalies or 

 alkaline earths, but this change is accompanied by simultaneous 

 loss of activity. 



The bark also contains fat (about 2 per cent.), glucose, and a hydro- 

 lytic enzyme. No difference could be detected in the chemical 

 constituents of the fresh (one year old) bark and the matured (three 

 years old) bark. Purshianin (Dohnie) and cascarin (Leprince) appear 

 to be impure substances. 



Cascara bark yields about 27 per cent, of aqueous extract and 

 5 per cent, of ash. 



Uses. Cascara sagrada is tonic and stomachic in small doses, 

 aperient in large doses, and cathartic if freely given. It is said to be 

 more active and more certain than alder buckthorn. 



Substitutes. The bark of It. calif ornicus, Eschscholz, is said to 

 have been substituted for that of R. Purshianus. The shrub occurs 

 sparingly in North California, but abundantly in the south and east 

 of the State, as well as in Arizona, New Mexico, and Texas. The 

 bark is said to be distinguished by its dull grey, slightly reddish cork, 

 its fewer lenticels and uniform coat of lichens ; the inner surface is 

 said to be paler, and the medullary rays commonly 3 to 4 cells wide, 

 those of R. Purshianus being only 2 to 3 cells wide. The two plants 

 are, however, so closely allied that some botanists refer them to the 

 same species. 



The bark of Rhamnus catharticus, Linne, also contains frangula- 

 emodin together with chrysophanol, rhamnosterin and a fluorescent 

 body, rhamnofluorin. 



