Evans (1947) has reported that treatment of sea water with X-radiation deleteriously affects the survival and activity of Arbacia eggs and sperm. This effect can be duplicated by H202 and can be completely negated by the addition of catalase. Such biological effects of irradiations have been studied in a number of laboratories (Barron et al., 1947; Giese, 1947). Stone et al. (1947, 1948) increased the mutation rate of Staphylococcus aureus to penicillin and streptomycin resistance by ultraviolet irradiation of the substrate prior to inoculation of the organisms. They suggest that the mutant individuals arise as a result of the assimilation of modified substrate molecules. A similar enhancement of the mutation rate results when the organisms are grown in a nutrient broth that has been treated with hydrogen peroxide prior to inoculation (Wyss, Stone, and Clark, 1947). Since very sensitive chemical methods failed to show any residual hydrogen peroxide at the time of inoculation of the treated broth, the mechanism appears analogous to the irradiation experiments. The similarity of the effects produced on proteins and peptones by H202 and radiations has been reviewed by Anow (1937). Fernau (1923) concluded that the results of a treatment with Roentgen rays, ultraviolet, and alpha particles on albumin solutions were identical with those produced by peroxide. Lieben (1927) states that the disappearance of the color reaction for tyrosine and tryptophan in proteinaceous solutions exposed to ultraviolet can be duplicated with H202. After the solutions stand for several days, the color reactions reappear. This process can be hastened by the addition of spongy platinum to decompose traces of peroxide in the solutions. However, Taylor, Greenstein, and Hollaender (1948) showed that the changes in viscosity of sodium thymus nucleate solutions that occurred following X-radiation could not be duplicated by H120 at 10-2 to 10-' M.

Cytogenetics has proved to be a valuable aid in the study of higher organisms but has received only limited attention in microbiology. Witkin

w i i w s i t y of Texas, Aiisli/iBased on the assumption that something other than the absorption of energy in the gene and the local change may be involved in tlie production of mutations by irradiation, attempts have been made to determine possible steps between irradiation of living organisms aitd resulting mutation phenomenon. Since some cheiitieal or phJ-sical change must be wespoiisible f o r the modification of the gene causing mutation, the possibility of obtaining gene cliangcs by inodifyiiig the food was explored. Strong evidence of a step bettreen tlie absorption of radiant eiiergv and the mutatiori process would be established if mutation could be produced by nourishiiig the organisms 011 an irradiated substrate (Stone, TTyss and Haas, '47).Demerce ( '45) has sliomrii that the drug-resistant individuals appeariiig in cultures of Staphylococcus CIUWZ(S arise AS a result of mutations. Such inutatioits occur at a low but readily measurable rate, which can be increased by irradiating the organisnis. It was found that ultraviolet irradiation of the medium in which the organisiiis are to be grow11 res;rultecl in manifold increase in the number of niutations. This occiirred with mutatioiia hot11 to penicilliii and t o streptoiiiycin resistance. XATERIBLS ASP METHODSFirst experiments were done with peptone broth but the phenomenon was also observed with a simplcr cheniically Talk dclirered by Dr. Stonr. 133

Laboratory and field experiments have shown that ultraviolet light may be as effective a treatment for microbial control in injection waters as many biocides. In many cases, the use of ultraviolet light is less expensive. The ultraviolet unit must be properly designed and constructed, and the effectiveness of the unit must be determined by a bioassay rather than by Ohysical measurements. Experimental results are presented and recommendations for design and use of ultraviolet units are given.

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