SENSITIVITY OF DROSOPHILA TO POISONING BY OXYGEN

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Abstract
The sensitivity of an inbred strain of Drosophila to poisoning by O2 was studied under a variety of exptl. conditions. 2 end-points were used to measure this sensitivity. In one group of expts. the length of time necessary for lethal effect was ascertained; in a 2d group, the toxicity was judged in terms of the duration of exposure necessary for the loss of spontaneous and reflex movements. The degree of recovery following non-lethal poisoning was detd. by comparing the frequencies of wing-beat during flight before and after treatment. High tensions of N were found to be without effect in protecting the tissues against the toxic effects of high tensions of O2. Marked increase in toxicity accompanies increase in O2 tension. Under standardized conditions the rate of O2 poisoning by 10 atmospheres of O2 was approx. 8 times that by 2 atmospheres of O2. The relationship between O2 tension and toxicity is linear on double logarithmic co-ordinates and consequently agrees with the usual form of time-concentration curves in pharmacology. The toxicity varied as approx. the 2d power of O2 tension. A similar type of relationship obtains for the symbiotic protozoa of termites, studied by Cleveland. For the protozoan, the toxicity varies as approx. the 4th power of O2 tension. These results suggest a general method for comparing in quantitative terms and under standardized conditions the sensitivity of other animals to O2 poisoning. The toxicity of high O2 tensions increases regularly with the temp. and presumably the metabolic rate of the tissues. At 34.2[degree] C. the rate of poisoining by 5 atmospheres of O2 was nearly 8 times as rapid as. at 14.4[degree] C. Evidence was found that young animals are more resistant to O2 poisoning than old animals. The significance of CO2 as the causal mechanism in O2 poisoning is discussed. The evidence does not support a general explanation of O2 poisoning in terms of accumulation of CO2 in the tissues, although such a process may be significant in animals containing Hb. The toxic properties of gas mixtures containing high tensions of O2 are enhanced as the CO2 tension increases. The toxicity of O2, as judged from these expts. on Drosophila, is therefore not solely a function of O2 tension. Among numerous other possible factors, the effect also depends on the temp., CO2 tension, and the age of the animal, all of which are known to affect metabolism. Thus O2 poisoning must be considered not only in terms of the reagent, the absolute tension of O2, but also in terms of the reactant, the biochemical metabolic processes in the tissues.

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