48 MEDICIXAL HEPvBS AND POISONOUS PLANTS 



oxalate of potassium may take place. The essential 

 points to note axe the following: — 



1. The production of oxalic acid in a relatively large 



qiiontity is an essential feature in the meta- 

 boiisin of the Khubai'b plant. 



2. This production takes place mainly in the leaves, 



probably from the oxidation of sugar; conse- 

 quently there will be a greater chance of finding 

 free oxalic acid in the leaf than in parts further 

 aAvay. 



3. The neutralization of oxalic axid is a paramount 



necessity to the plant, and this is accomplished 

 before the product is carried away down the 

 leaf-stalk, 



4. A probable second source of danger is the fact 



that instead of calcium the neutralization may 

 be accomplished through the agency of potassium, 

 the compound of oxalic acid with the latter being 

 highly poisonous. (The active principle in the 

 poisonous salts of le^^non is a compound of potas- 

 sium and oxalic acid, namely binoxalate of potash.) 



Finally, it may be noted that in boiling the plant 

 with water containing baking or w^ashing soda there is 

 always a risk that chemical changes may take place,' 

 involving the removal of the calcium from its beneficent 

 combination w^ith oxalic acid, in wdiich Cfise poisonous 

 results would follow, either from the acid itself or from 

 the substance formed by its new alliance. Whatever 

 the theoretical explanation may be, the fact remains, 

 after many trials, that rhubarb leaf-blades are baneful 

 in their effects, and that, except for a very few people, 

 • rhubarb leaf-stalks can be eaten not only witli enjoy- 

 ment but also with digestive profit. 



The Polygonum Gkoup. — Distinmii^hed from the 



