Extraction of house-fly heads with neutral phosphate buffer yielded a dark brown solution from which a number of pigments were separated, either wholly or partially, by chromatography on a column of calcium phosphate mixed with celite. One of the pigments was light-sensitive, and had a yellow color, with a spectral absorption maximum at 437 mµ in phosphate buffer at pH 6.5. Several consecutively eluted fractions from each chromatogram of the house-fly head extract showed the characteristic absorption curve of this pigment with no trace, spectroscopically, of the other pigments of the extract. The products of bleaching the pigment at pH 6.5 had an absorption curve showing plateaus at 440 to 460 mµ and 350 to 360 mµ and an inflection at about 250 mµ. Above pH 8.0 the pigment bleached in the dark giving an absorption maximum at about 380 mµ, and inflections at 290 mµ and at about 250 mµ. With 2.5 to 5 N HCl or H2SO4 an absorption maximum at 470 to 475 mµ was obtained with either the unbleached or the bleached pigment. With sulfosalicylic acid, ethanol, or heating at 100°C., a part of the pigment was precipitated, leaving a light-stable yellow supernatant.

This light-sensitive house-fly pigment cannot as yet be identified with any of the previously known insect pigments or with the photosensitive pigments of other animals, though these latter compounds exhibit some similarity in their spectroscopic properties.

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