BY JAMES M. PETRI B 539 



which follows the sting. For a long time after, the pain keeps 

 returning whenever the injured part is wet. The Hon. W. 

 Pettigrew records a case (2) where the pain continued to be felt, 

 under these conditions, after the lapse of a month from the sting. 

 An occasional companion of the dreaded stinging tree is the 

 small plant Colocasia macrorrhiza, which the aborigines call 

 " cunjevoi." This large-leaved plant is sometimes found growing 

 round the nettle trees and is used as an antidote and painkiller, by 

 rubbing on the affected part for an hour or more. In a note to 

 Pettigrew's paper mentioned above, I find it stated that the inner 

 bark of the Laportea itself contains an antidote to its sting. An 

 interesting fact, which may possibly be associated with this 

 antidote, is the occurrence of numerous crystals of calcium oxalate 

 in the bark, first observed by H. G. Smith, of the Technological 

 Museum. 



The Metabolism op the Plant. 



Occurrence of Organic Acids. — They occur (1) free, (2) combined 

 with inorganic bases, with which they frequently form acid-salts, 

 (3) combined with organic bases, as alkaloids, glucosides, or other 

 vegetable principles. 



The first six acids of the acetic series have been met with in 

 plants(3). Acetic acid in minute quantities occurs in the sap of 

 a great many plants both free and as esters or salts. Formic 

 acid is of very rare occurrence(4). Its existence was first dis- 

 covered in the common nettle in 1849, by Professor Gorup- 

 Besanez of Erlangen(5), the acid nature of the fresh sap having 

 been noticed shortly before by Lucas, an apothecary of Arnstadt. 

 It is also present in pine needles, where it is probably the result 

 of the oxidation of terpenes, and in the wood of Goupia tomen- 

 tosa(6). Neutral formic esters exist in the juice of the house-leek, 

 in the fruit of the soap-tree (Sapindus) together with butyric 

 acid compounds, and in tamarinds associated with acetic and 

 butyric compounds. It seems quite possible that the tartaric 

 acid in these fruits may have oxidised and formed formic and 

 acetic esters, since these changes can easily be brought about 

 artificially by slow oxidation. 



