Note of a New and Apparently Useful Biological Indicator of X-ray Dosage

Abstract

IT HAS long been recognized that fundamental investigations of the physiological effects of electromagnetic radiations of high quantum energy are very largely dependent, on the biological side, upon the availability of suitable test objects. Such test objects should be small in volume but of such size as to be readily visible to the naked eye so as to minimize the technical difficulties involved in the examination of large numbers; should be available in such quantities as to be adaptable to long-range statistical investigations involving large populations; should be genetically and physiologically standardized to as great an extent as possible, and should, above all, present sharp and unmistakable end-points as criteria of effect. A very considerable range of material has been explored in the past in an extensive effort to locate and standardize such a tool. Probably nothing has been found more generally adaptable and suitable for fundamental investigations in the biological effects of x-rays and cathode rays than the ova of the fruit fly, Drosophila melanogaster. The technic of rearing and handling the flies, isolating, raying, and observing the eggs has been extensively described by Packard (1), P.S. and C.T. Henshaw (2), Glocker and his collaborators (3), and others, and is well known. So far as is known to the authors, failure of the larva to emerge from the egg, or abnormalities of embryonic development have been the criteria of effectiveness used, and wild-type stock has been employed in every case. For several years the writers have been engaged in a reasonably extensive statistical study of the incidence of mosaic colorless patches in the ommatidia of the compound eyes of adults of eosin Drosophila melanogaster x-rayed as eggs or very young larvæ, continuing an investigation initiated by Patterson (4), in 1929. A study was originally undertaken of the frequency distribution of mosaics of white eye color, resulting from somatically affected cells of the eye anlage, in an x-rayed population as a function of the incident energy input. The original purpose of the work was to so treat the data as to give information, first, of the number of ion passages required to traverse a given genic locus to achieve the desired effect, and second, the magnitude of the volume or aggregate of volumes in a cell within which the “hit” must occur. After considerable acquaintance with the material, however, the authors have come to feel that it presents a sufficient number of unusually desirable characteristics as a biological indicator of x-ray dosage to be possibly worthy of wider application in therapeutic work. The effect sought presents a sharp, reliable, and readily observed end-point, its frequency of occurrence varying with x-ray dosage at a single series of wave lengths in so direct a fashion as to indicate that a rather simple effect may be involved.