Abstract
The study of ingestion in Paramecium is ordinarily accompanied by considerable difficulty due to the fact that there is little difference in color between the animal, the surrounding medium, and the bacteria which serve as food. The following method differentiates these elements by means of contrasting colors.
The dye used in this investigation was acid fuchsin, certification number NR-2, having a dye content of 62%. Solutions were prepared with distilled water so that their described percentages represented the actual dye strength.
Two drops of culture fluid containing large numbers of paramecia were placed on a clean slide, a drop of 1% solution of acid fuchsin added, and a cover glass applied. The fluid formed a thick layer under the cover glass, but the dye solution was unequally distributed. The preparation was allowed to stand undisturbed for one or 2 minutes, then examined under low magnification with reduced light. The paramecia, under these conditions, appeared to be outlined sharply in black. A portion of the fluid was then drawn off by the application of a strip of filter paper, thus reducing the thickness of the film of solution under the cover glass. In this thinner layer paramecia appeared to be colored a pale, luminous green, the color being deeper in those animals which had spent some time in the more deeply colored portions of the preparation before swimming out into the lighter areas. It must be emphasized here that this color phenomenon appears only when the amount of liquid under the cover glass is small; it will not appear if the cover glass “floats high.”
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