A Determination of the Magnitude of the Cell “Sensitive Volume” Associated with the White-Eye Mutation in X-Rayed Drosophila—

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Abstract
A redetermination was made of the volume associated with the white-eye mutation in D. melanogaster, following methods earlier described by one of the authors (Proc. Nat. Acad. Sci. U. S. A. 21(10): 561-566. 1935) in addition to which 2 new points have been added to the curve and the probable errors of existing points greatly reduced. Both sets of data agree within less than their respective probable errors. The average volume of the individual locus for white eye is calculated as 2.32 X 10-18 cc, corresponding to a radius, assuming the locus to be spherical, of 8.21 X 10-7 cm., of which only the order of magnitude is considered significant. The number of cells in the optic anlage has been directly determined by cytological count, instead of by ratios of affected to total ommatidia of the adult eye, as in the earlier paper. This refinement does not appreciably alter the results. The value for the volume agrees reasonably well with determinations for the volume of a gene made by Morgan, Blackwood, and Gowen and Gay, and with Marshak''s value for the diam. of a chromonema in Gasteria. The radius is of the same order of magnitude as that given for the insulin molecule by Sjogran and Svedberg, the trypsin molecule by Northrop and Kunitz, and the albumen molecule by Svedberg and Sjogran, and Nichols. It is smaller than the radius of the hemocyanin molecule as detd. by Svedberg and Chirnoaga.