OF INSECTS. 145 



a threefold purpose : 1st, 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 ihat 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. Hurnboldt 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 esophagial 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- 



