THE HARVESTING ANTS. 293 



to extend along the limbs for some distance and to settle in the lym- 

 phatics of the groin and axillae. If it be true, as has been reported, 

 that the ancient Mexicans tortured or even killed their enemies by 

 binding them to ant-nests, P. barbatus was certainly the species em- 

 ployed in this atrocious practice. It is commonly supposed that the 

 poison responsible for the pain inflicted by these and other ants is 

 formic acid, but chemical analysis of P. molefacicns by Melander and 

 Brues ; 1906) failed to reveal any traces of this substance. Hence the 

 poison of this insect must be some unknown substance, possibly a 

 nucleoalbumin. This confirms the opinion of other authors, who, like 

 Fiirth (1903), deny that the general physiological effects of the sting, 

 even in the European ants, are due to formic acid. 



