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To the Editor.
—Toy balloons with imprinted figures that make them suitable for use as opticokinetic testing drums are readily available. I have been using them for this purpose for some time and find them very effective. They have the obvious advantage that in the deflated state they occupy only a fraction of the space required by the usual drum and are readily portable. In use they are most easily controlled by sticking a loop of plastic tape to the end opposite the stem to use in rotating the balloon as a drum. A florist "twistem" wire is very handy for sealing the stem while the balloon is inflated for use.