144 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 rtifa 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 . That which they 
ejaculate from their anus when attacked, as formerly 
stated f , must be secreted in an ioterium ; but their very 
blood seems of an acid nature. It is very probable, as 
Dr. Thomson has observed s , that acids may be obtained 
from many other insects, and that they are various mo- 
difications of the acetic. 
* Philos. Trans. Ibid. Ray's Lett. 74. 
h Amoreux Ins. Venim. 236—. c N. Diet, a" Hist. Nat. xii. 94. 
A South ey's Brazil, i. 645. * N. Diet, a" Hist. Nat. ubi supr. 
1 Vol. II. p. 67. ' Syst. of Chemist. 533. 
