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DURING radiobiological work on bacteria it was found by one of us (H. L.) that the effect of ionizing radiation (X-rays) is greatly potentiated if the bacteria are irradiated in a medium in which water is replaced by heavy water1. Thus, for example, with Escherichia coli B and Pseudomonas 6009 the dose-reduction factor was approximately 2, that is, the X-ray dose required to produce a given reduction in the number of colony-forming bacteria on irradiation in deuterium oxide was one half that in water. This effect, however, occurred only if the bacteria were irradiated in presence of oxygen, but not, or only insignificantly, after irradiation under anaerobic conditions.

SIGNIFICANT differences of the normal metabolism of tissues either in Ringer bicarbonate or in phosphate solution have so far not been reported1,2. On the other hand, the contradictory results obtained by Dixon and Elliot3 and Alt4 respectively concerning the hydrogen cyanide stable residue of the respiration of liver slices have been explained by the use of different media. Nearly complete inhibition occurs in Ringer bicarbonate while a considerable residue remains in phosphate solution or in Ringer without bicarbonate.

Two strains of yeast, a haploid and a diploid one, were irradiated with x rays, and survival curves were obtained by colony counts. In haploid yeast, the viability decreased exponentially with increasing x-ray dose, whereas the diploid strain exhibited a plateau in the dose-response curve similar to that previously described by other workers for haploid yeast. The number of survivals and the shape of the survival curves varied with the physiological condition of the cells at the moment of irradiation. Thus, for example, in baker's yeast, deprivation of a source of nitrogen prior to irradiation resulted in a certain degree of protection, when compared with the survival of fresh nonstarved cells. Considerable protection was further afforded in both strains of yeast if cells were grown and irradiated in high concentration of substrate (55% fructose). Lastly, nitrogen deprivation interposed between irradiation and plating also favored recovery. Reasons are suggested for these changes in support of the view that indirect effects of irradiation contribute to a large extent to loss of viability in yeast. (auth)

THE occurrence of a haemolytic substance in normal blood has been demonstrated by Bergenhem and Fahraeus1. This substance was present in the ether precipitate of the alcohol-soluble fraction of serum, and was described by them as a lysolecithin, that is, a derivative of lecithin from which one fatty acid has been split off by the action of lecithinase, an enzyme analogous to that contained in cobra venom. However, the evidence in favour of the existence of lecithinase in serum and of the lysolecithin nature of the lytic substance was indirect, since no attempt at purification or isolation of either the lecithinase or the lytic principle has been reported.