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. BIOLCGP AND MEDICINE Cytogenetics. Wgen, by itself,will break chromosomes and came chromosomal aberrations i n pollen grains of the plant Tradescantia; the effect is indistinguishable from that caused by radiation. work suggested t h a t the oxygen did not cause chmmosome'breakage directly, but acted indirectly by stimulating cellular reactions which in turn caused the breakage. known e n p e inhibitors such as cyanide, carbon monoxide, and low temperatures were tested for effect. of chromosomes by oxygen, These same factors have no effect, ora diffe rent effect o on radiation-induced breakage. that, in an oxygen atmosphere, the chromosomal breakage is.-induced.by a physiological reaction of the cells themselves. This idea was confirmed by experiments in which All strongly inhibited the breakage The results demonstrate Some years ago it was reported that Paramecium aurelia was less sensitive to the induction of genetic changes by ionizing-ion when treated in a period of about one hour before visible division of the cytoplasm of the cell than when treated at other times. It has now been shown that this insensitive period includes the whole prophase stage in the division of the micronucleus. metaphase and anaphase stages i s not yet certain. Whether it also includes the later The form of the dose response is different from that of the sensitive period, which includes all o r nearly all the interphase, the stage between divisions of the micronuclei. Thus t h e magnitude of the difference in sensitivity cannot be adequately represented by a single given by stating that a dose of about 20,000 r is required during prophase t o produce the same effect as 1,~OO r during interphase, However, some appreciation of the very g r e a t difference can be Radiation Protection. Marked progress was made in the last two months i n studies on the mechanism of protection of Escherichia c o l i from the lethal effects of ionizing radiation by cysted-c-eremarkable radiation resistance t o E. coli. It was shown that the greater part of the protection affoFhed by this compound i s probably due to an interaction of cysteamine with the bacterial cell which leaves a much greater proportion of the cells able t o recover from the effects of a given dose of radiation when supplied with certain nutrients*or gram ata favorable temperature (18OC as opposed t o 37OC). required f o r recovery are found i n yeast extract, beef broth, and other. Data were accumulated which indicate t h a t cysteamine gives
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natural extracts. A chemically defined growth medium which promotes , recovery of unprotected, irradiated cells will also support recovery of cysteamine-protected, irradiated cells. This medium contains, in . addition t o inorganic salts and glucose, an amino acid, glutamic acid; a purine, guanine; and pyrimidine, uracil. structure to activity in radiation-protective compounds, a new series of isothiouronium salts, related top-mercaptoethylamine, were prepared. I n addition, most of the previously reported compounds were tested f o r protective effects in C57BL mice subjected t o 900 r total body x radiation. A new compound i n the thiouroniwn series, SoB-aninoethylisothiouronium bromide HBr, proved t o be a t least as effective as#?-memaptoethylamine and appeared t o be l e s s toxic, raising the LD50 from 750 r to 1150 re Other derivatives (250 mg/kg) which did not decrease .the radiation-induced mortality b u t enhanced the survival time include N-acetyl and N,S-diacetylp- mercaptoethylamine , b i s 09- aminoethyl) disulfide and S,S-ethylenediBiochemistry. I n the continuing study of the relation of Plant Biochemistry. Green plants and c hbro p lasts have previPo-ously been shown t o emit light for a shorti time after ill mi nation. tassium ferricyanide, which is a strong oxidizing agento was found t o suppress this light emission i n chloroplasts. The intact barley plant tions of C%. Exposure of the pf a n t t o carbon monoxide prolongs the . period of light emission. fixation and.-!exposure t o carbon monoxide stbdates light emission, it 2s believed that the carbon ioxide fixing process is i n competition with Since carbon monoxide is known to inhibit CO the production of delayed light. 1 Biophysics. Tradescantia inflorescences and dry pollen were exposed t o fast neutrons i n the facility at tihe 86-~nch Cyclotron, curves for 4-day chromosome aberrations' i n the microspore division, as well as chromatid aberrations i n the pollen-tube division, were obtained, The pollen experiments a l s o included comparison control treatments (200 r) by 250-kv x rays and by cobaltyrays, These studies, based on recent neutron dose measurements in the cyclotron facility, indicate a relative biological effectiveness for fast neutrons relative to cabal%)' rays of approximately 10 for 4-day chromosome aberrations and 8for
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BTOLCGY AND MEDICINE Pathology and Physiology. Experiments i n progress suggest a relation between the throid-pituitary axis and the susceptibility of AK-strain mice t o transplants of lymphoid tissue from'leukemic mice of the same strain. thyrotrophic hormone and thyroxine injections proved t o be more susceptible t o transplanted tumor tissue (83 percent deaths after 2 weeks) than treated controls (20 percent mortality), thyroidectomizedthyroxine injected (50 percent mortality), and uninjected thyroidectomized mice (20 percent mortality), of the relation between the hormones involved and the susceptibility A series of radiothyroidecbmized mice receiving It remains to establish the nature Enzyme Chemistry. The decay curve for the delayed light from green plants was originally studied from 0.25 seconds t o 10.0 seconds. By t h e use of a rotating section phosphoroscope this study was extended t o periods dawn to 0.002 secondso suspensions of Chlorella the decay was followed f o r as long as 100 minutes. ,Over this wide range, the delayed light falls off approximately By using very large volumes of Effects of polonium on EScperimental Animals. It has been determined in single dose studies at Mound Laboratory that 0.5 uc/kilo dose of polonium,administ.ered intravenously, will reduce the life span by 15 percent inthe rat and result in an estimated dose of 16 rem t o the kidney, critical organ as identified by Mound, of 20, however, and utilizing the observed ability of the kidney t o concentrate polonium as compared with other organs and tissues of the rat, the t o t a l dose is estimated t o be about 3000 rem to the kidney during Approximately three times the Mound Laboratory rpaximal permissible body burden of polonium has been maintained i n experimental rats through monthly injections. The chronic dose experiment has proceeded over a period of 30 months. The body burden maintained in t h e experimental animals is 0.01 uc/kilo. the experimental animals are within 25 percent of t h e calculated body retention. The results from the experiment show t h a t 3 x , .the maximal permissible body burden, gives an ineffective dose t o the laboratory Organ and carcass analyses on
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BIOLOGY AND MEDICINE Effects of Actinium on Experimental Animals. 0.2 uc/kilo, total alpha, injected monthly into laboratory rats is being applied t o determine effect on life span and tumor production. It is now certain that a rather typical osteogenic sarcoma can be expected a t about 20 such doses, or 20 months. The tumor appears predominantly i n the lumbar It can be produced i n single-dose experiments a t 300 days A striking effect of actinium and its products may be found in the young i f the material is given the mother prior to birth. 3 uc/kilo of actinium administered 1.V. a t 4-7 days before birth will give almost 100 percent lesions i n the young. A small amount of placental transfer occurs of actinium, b u t primarily the effects are due t o short-lived radium delivered t o the young via the milk, the major portion of t h e actinium being retained i n the bones of the Cesium Teletherapy Unit. The IT. F. and John Barnes Cornpaw designed and bui lt a cancer therapy unit t o specifications of the OIUNS direct a pre-set treatment pattern, was unveiled.at Rockfort, Illinois, July 22. The u n i t and its radiation source, cesium, will be thoroughly tested before it becomes available for the treatment of patients. The machine, with a built-in computing device t o