. Bulletin - Biological Survey. Zoology, Economic. LABOEATOEY EXAMINATION OF STOMACHS. 13 beaker. The beaker is then held under a faucet, so that the rush of water will cause whatever insect remains tciSjJ be present to float to the surface, where they can be decanted oft* with a filter of bolting- cloth. The remaining matter in the beaker (generall}^ seeds and fruit skin) is then collected on another filter, and from the two filters the material is transferred by means of a scalpel to separate smooth blot- ters about o inches square, and is ready for examination. Examina- tions are usually ma
. Bulletin - Biological Survey. Zoology, Economic. LABOEATOEY EXAMINATION OF STOMACHS. 13 beaker. The beaker is then held under a faucet, so that the rush of water will cause whatever insect remains tciSjJ be present to float to the surface, where they can be decanted oft* with a filter of bolting- cloth. The remaining matter in the beaker (generall}^ seeds and fruit skin) is then collected on another filter, and from the two filters the material is transferred by means of a scalpel to separate smooth blot- ters about o inches square, and is ready for examination. Examina- tions are usually made with a dissecting microscope furnished with an achromatic triplet lens, but occasionally it is necessary to emploj^ the liigher powers of tlie compound microscope. The ijrincipal difficulty arises from the fact that birds often mutilate their food before swallowing it, and the gizzard afterwards reduces it to fine fragments. A song sparrow, for exami)le, will seize a grass- hopper, pinch it a dozen times, pull off and eat the head, pull off the legs and wings and then swallow the abdomen, leaving the otlier 13arts. In the gizzard, with its powerful muscular walls, the reduc- tion of the insect is more complete, so that usually within two hours only a few bits of grasshopper dust remain. It is with such ma- terial that the examiner has most often to deal. But with practice iiis eye quickly detects amidst tliis dust a squarish, bicolored jaw with a grooved cutting-edge behind which is a grinder (see PL II, fig. 1). If the jaw is lacking, a little search seldom fails to re>^eal a tiny piece that looks like a human ear, but in reality is part of the knee-joint of the grasshopper (see PI IT fi<J' ']\ Pig. 7.—Jaw of May-beetle ' ^' '' (top and side views I. The remains of caterpillars found in bird stom- achs usually consist of the discolored broken skin, which has been twisted and rolled into compact little packets by tlie action of the stom- ach. Sometimes nothing is lef
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