INTERNAL ANATOMY OF INSECTS. 137 
the animal feeds, and which therefore would seem to un- 
dergo but little alteration. 
Wax seems also to form a constituent part of some 
insects which are not found to secrete it. The yellow 
substance deposited in vessels containing spiders in al- 
cohol is said to be a true wax, and may be obtained from 
these animals by gently heating them?. 
ix. Pozsons and Acids. The bite as well as the sting 
of many insects is followed by inflamed tumours, so that 
the séalisteria of some bugs, Diptera, Aptera, and spiders, 
may be regarded as producing a poisonous fluid; but we 
know nothing of the real nature of it, nor of that of other 
venomous insects, except the azt—whose celebrated acid 
may be considered under the present head,—the dee, the 
wasp, and the scorpion. 
Contrary to the once received doctrine that no acid 
was to be found in any animal, except as the effect of 
disease in the alimentary canal, many insects secrete pe- 
culiar and powerful ones. I have on a former occasion 
related an instance in which an acid of this description, 
secreted in its s¢alisterza, is employed by a moth to soften 
its cocoon®; and Lister mentions a species of Julus which 
produced one resembling that of ants‘; but this last is 
the most powerful of all. The fact that blue flowers 
when thrown into an ant-hill become tinged with red has 
been long known; but Mr. Fisher of Sheffield, about 
1670, seems to have been the first who ascertained that 
this effect is caused by an acid with which ants abound, 
and which may be obtained from them by distillation or 
infusion in water4. Margraff and other chemists con- 
* Nicholson’s Journ. i. 298—. » Vor. IIT. 283. 
© Philos. Trans. 1679. 4 Jbid. Ray’s Lett. 74. 
