138 Proceedings of the Boyal Society of Edinburgh. [Sess. 
* 
acid having come from the stinging hairs of the nettles, as distinguished 
from the general plant tissue, cannot be regarded as settled by the 
experiments of Gorup-Besanez, even were it admitted that this acid 
had been definitely proved to be present in the distillates which this 
investigator obtained. 
In a paper by Haberlandt,* in which the poison of the stinging hairs 
of the nettle is dealt with at considerable length, the author simply accepts, 
without making any attempt to prove it, the view that the strongly acid 
reaction of the liquid ejected on breaking the tip of a stinging hair may 
be due to formic acid, but holds that the quantity of this acid which could 
be present is insufficient to account for the degree of irritation produced 
by the sting ; and he supports this opinion by pointing out that when the 
contents of a stinging hair were permitted to become quite dry on the 
point of a needle, whereby he assumes that any formic acid which was 
present would be volatilised, the subsequent pricking of the skin with the 
needle point produced, after a few seconds, the characteristic stinging 
sensation as well as reddening of the skin at the spot. Haberlandt’s 
investigations, in which the contents of the stinging hairs were sub- 
mitted to an elaborate micro-chemical examination, led him to the 
conclusion that the active poison is most probably a substance of the 
nature of an enzyme. 
Harvey Gibson and Warham j* did not find any evidence of formic acid 
in the stinging hairs of the nettle, and as the result of their experiments 
they were at first inclined to consider that tartaric acid is the irritant 
substance which these hairs contain. Towards the close of their short 
note, however, they state that they hazard no conjecture as to the 
chemical nature of the substance, but reserve their conclusions for a 
further note. Endeavours to trace any further note by these authors 
have not been successful. 
In a paper “ On the Stinging Property of the Giant Nettle Tree” 
(Laportea gigas), Petrie, J when comparing the amount of acid obtained 
by distilling 100 grams of the fresh leaves of this plant in a current of 
steam in presence of phosphoric acid with the amount obtained by the 
same process from 100 grams of the fresh young leaves of the common 
nettle ( TJrtica urens), estimated the latter at 0*002 per cent., but apparently 
assumed, without applying any test to the distillate, that the acid obtained 
in the case of the nettle was formic acid. 
* Sitzungsber. der Akad. der Wissenschaft. Wien, vol. xciii, 1. (1886), p. 130. 
t Proc. Liverpool Biolog. Soc., vol. iv (1890), p. 93. 
I Proc. Linn. Soc. N.S. Wales, vol. xxxi (1906), p. 530. 
