Page:Jardine Naturalist's library Entomology.djvu/151

Rh 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 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 inflammation 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. Burmeister 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 imbibing the peculiar juice with which this cavity is replenished. This juice is nearly transparent in herbivorous 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