Some Effects of X-Ray Irradiation on Respiration and Development. ∗

In much of the previous work on the biological effects of X-rays morphological criteria alone have been used. It is, therefore, impossible to tell whether certain end-points are reached in similar or far different manner. This report states briefly the findings of a study of the effects of different intensities of irradiation on the oxygen consumption and development of the larva of the Muddauber Wasp Sceliphron caementarium.

The method used to separate latent-developing (diapause) larvæ from the developing organisms has been described. 1 Correlations between the morphological stages in development and the respiratory curve are also pointed out.

Four distinct morphological and physiological stages are distinguished—larva, post-larva, pre-pupa, and pupa. When the diapause factor is present the organism remains normally in the quiescent larval stage for several weeks before developing. Such organisms when irradiated with 300-400 R. Units at the beginning of diapause remain in that condition several weeks longer than the controls. Higher intensities of irradiation (600-700 R. Units) shorten, and may even destroy the diapause factor, allowing the larva to develop at once. Still higher intensities (800-1500 R. Units) destroy diapause and permit of development which is subsequently inhibited.

Organisms in which the diapause factor is no longer present are accelerated by irradiation of 300-400 R. Units. The respiratory rate is higher and the time required to reach the pre-pupal stage is much shorter than in the controls. Six hundred to 700 R. Units inhibit, and 800-1000 R. Units are lethal before the pupal stage is reached.

Irradiation may affect (within limits) the physiological stage, active at the time of the treatment, without affecting following stages. If the physiological stage, dominant at the time of irradiation, is of such a character as to he antagonistic to development, then the response is not only quantitatively different from that of the developing stages, but will he apparently opposite in nature.