14-4 INTERNAL ANATOMY OF INSECTS. 



infusion in water a . Margraff and other chemists con- 

 firmed this discovery b ; and concluding that this acid 

 was of a peculiar kind, they gave it the name of the For- 

 mic acid. This name, however, is now exploded ; the 

 subsequent experiments of Deyeux, Fourcroy and Vau- 

 quelin having ascertained that the acid of ants is not of 

 a distinct kind, but a mixture of the Acetic and Malic c . 

 These acids are in such considerable quantities, and so 

 concentrated in these animals, that, when a number of 

 Formica rufa are bruised in a mortar, the vapour is so 

 sharp that it is scarcely possible to endure it at a short 

 distance. It also transpires from them, for they leave 

 traces of it on the bodies which they traverse: and hence, 

 according to the experiments of Mr. Coleridge, the vul- 

 gar notion that ants cannot pass over a line of chalk is 

 correct ; the effervescence produced by the contact of 

 the acid and alkaline being so considerable, as in some 

 degree to burn their legs d . The circumstance of much 

 of the food of ants being of a saccharine nature may ac- 

 count for this copious secretion of acid, the use of which 

 is probably to defend themselves and their habitations 

 from the attack and intrusion of their enemies : if a frog 

 be put into a nest of Formica rufa that has been deranged, 

 it will be suffocated in five minutes e . That which they 

 ejaculate from their anus when attacked, as formerly 

 stated f , must be secreted in an ioterium s but their very 

 blood seems of an acid nature. It is very probable, as 

 Dr. Thomson has observed 5 , that acids may be obtained 

 from many other insects, and that they are various mo- 

 difications of the acetic. 



a Philos. Trans. Ibid. Ray's Lett. 74. 



b Amoreux Ins. Venim. 236 . c N. Diet. a" Hist. Nat. xii. 94. 

 d Southey's Brazil, i. 645. e N. Diet. d'Hist. Nat. ubi supr. 



f VOL. II. p. 67. * Syst. of Chemist. 533. 



