OF INSECTS. 
145 
a threefold purpose : 1 st, The mechanical dilution of 
the nutriment; 2d, to exercise a chemical effect 
upon it ; and 3d, a dynamical effect ; or, in other 
words, to change the food into such a state that the 
requisite nutrimental substances can be separated 
from it. The chemical properties of the saliva have 
been but little investigated ; that their action is 
powerful may be conjectured from the pain and in- 
flammation produced by the puncture of a Culex or 
Tabanus, which is almost wholly occasioned by the 
saliva injected into the wound. The effect it has 
upon the leaves eaten by caterpillars is to make 
them almost immediately lose their colour, and 
assume a dirty brownish tint. Humboldt affirms 
that the saliva of serpents of itself suffices to change 
the flesh of recently killed animals into a gelatinous 
substance, and that it is for that reason they lick 
their prey all over before they swallow it. Bur- 
meister is of opinion that it has a similar tendency 
in insects; at all events, there can be little doubt 
that its effects are not limited to a simple lubrication 
of the parts of the mouth, or a mechanical solution 
of the particles of the food. 
After passing through the csophagial tube, the 
alimentary matter reaches the crop, where it remains 
for a time, and acquires a softer consistency by im- 
bibing the peculiar juice with which this cavity is re- 
plenished. This juice is nearly transparent in her- 
bivorous insects, but dark and fetid in the carnivora, 
as is- often experienced by insect-collectors, for it 
is this matter which the animals so frequently dis- 
K 
