INTERNAL ANATOMY OF INSECTS. 149 
. In oilier cases these odours are produced by gaseous 
vapours. That of the Bombardiers (Brachinus) is the 
most celebrated and remarkable. It is whitish, of a 
powerful and stimulating odour, very like that exhaled 
by nitrous acid. It is caustic, producing upon the skin 
the sensation of burning, and forming instantly upon it 
red spots which soon turn brown, and which, in spite of 
frequent lotions, remain several days. It turns blue 
paper red a . That amiable, intelligent, and unfortunate 
traveller Mr. Ritchie, — whose premature death, when at- 
tempting to penetrate to the interior of Africa, all lovers 
of Natural History so deeply lamented, and whose ardour 
in the pursuit of that science I had an opportunity of 
witnessing, when, in company with him, Messrs. Savigny, 
Du Fresne, and W. S. MacLeay in 1817, I visited the 
forest of Fontainebleau, — in a letter to the last-mentioned 
gentleman b , relates that his companion M. Dupont, near 
Tripoli took a nest consisting of more than a thousand 
of a species of this genus. " I am making a few experi- 
ments," says he, " on the substance which they emit 
when they crepitate, but do not know whether I can col- 
lect enough to arrive at any conclusion. It made Du- 
pont's fingers entirely black when he took them. It is 
neither alkaline nor acid, and it is soluble in water and 
in alcohol." From this we may conjecture that it formed 
crystals. 
xi. Phosphorus. On this remarkable secretion I have 
so fully enlarged on a former occasion c , that here I shall 
merely add a few observations which Mr. Murray obli- 
a N. Did. (VHist. Nat. iv. 308. 
b Dated Tripoli in the West, January 21, 1819. 
r Vol. II. p. 418—. 
