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The course of N-NO 3 concentrations in soil, N transfer from the catch crops Vicia sativa L. and Trifolium resupinatum L. to the companion grass Lolium multiflorum ssp. gaudinii (Parl.) Schinz et Keller, and the preceding crop effect on Lolium multiflorum ssp. italicum (A. Br.) Volkart were studied in a field experiment. Catch crops were sown in pure stands and grass/legume swards (= two species in alternating rows) at two sowing dates and harvested at different dates from August to November. Vicia sativa was more effective concerning N 2 fixation than Trifolium resupinatum, this was also evident from above ground N yield and N-NO 3 amount of the soil. The factor sowing date had the greatest influence on N yield. N transfer to the companion grass was generally low. Early sown legumes in pure stands and in mixture temporarily caused slightly increased N-NO 3 amounts in soil compared with unfertilized grass in winter and following spring, whereas late sown legumes apparently had no effect on N-NO 3 amounts. Both legumes had a considerable preceding crop effect in the mixture and in the pure stand for both sowing dates.

To investigate normal light scattering and cataract formation, the anterior eye segments of farmed Atlantic salmon (Salmo salar) reared in fresh water and sea water were documented in vivo for the first time with a Topcon SL-45 Scheimpflug camera. A total of 40 fish from the fresh-water-rearing period, obtained from 2 groups of identical age but showing a different growth rate, and 24 fish from the sea-water-rearing period, sampled from 2 groups with identical age but being fed different food brands, were included in this study. The fish were anaesthetized before examination. Due to the naturally wide pupil, no mydriatic compound was applied. All fish were removed from the water for photography, which was performed for each eye in 0° = vertical slit position. Images were recorded on Kodak Tmax 400 black-and-white film. Microdensitometric image analysis of all negatives was performed using a Joyce-Loebl online microdensitometer. In spite of the virtual absence of an anterior chamber gap between cornea and lens and very little light scattering in the normal fish lens, a small number of distinct layers could be reproducibly identified in the lens. While there was little abnormal light scattering which could point to cataract development in young fish from the fresh water period, the evaluation of the lenses from the 2 sea water groups showed the presence of specific forms of cataract especially in the cortical and supranuclear layers. There were significant differences between the groups fed different food brands at the sea water site. In conclusion, Scheimpflug photography proved to be applicable to eye research in fish in vivo. It is suggested that this method should be employed for reproducible documentation as an extension to slit lamp monitoring in experimental research to reveal causative factors for cataracts in farmed fish.

Micrococcus radiodurans , a red-pigmented bacterium, is very resistant both to ionizing and to ultra-violet radiations. The dose-response curves in both cases are sigmoidal with high extra-polation numbers. Two non-pigmented mutants of M . radiodurans have been isolated. One of these shows the same type of survival curve as the wild type while the other has an exponential survival curve. Energy transfer reactions including the possible role of pigment have been excluded as a mechanism of resistance. Similarly, resistance is not due to unusual amounts or unique properties of the bacterial DNA . Survivors of both sensitive and resistant bacteria show a lag period following irradiation. In the case of sensitive bacteria no change occurs in the radiosensitivity of the cells during this period. On the other hand, M . radiodurans recovers during the lag period, at the end of which it has become as resistant as the unirradiated cells. All available evidence for the loss of viability in bacteria points to DNA as the target. Recovery of M . radiodurans from radiation damage, therefore, is concluded to be due to repair of damaged DNA by an active cellular, probably enzymic process which occurs during the lag period. The large shoulder of the survival curve and the high extrapolation number are a reflexion of the efficiency of the repair system. The significance of the sigmoidal and exponential survival curves of resistant bacteria is discussed and a theory put forward which postulates two types of damage to the genetic structures, each having a specific repair system. Some experimental evidence in support of this theory is produced.

Most of the work on the effect of fertilization on the metabolism of seaurchin eggs has been concerned with the average rate of O 2 consumption before and after activation. Although observations of this type are of interest, the changes which take place during the actual fertilization of the eggs are more indicative of the mechanisms responsible for the initiation of development. Technical difficulties have impeded experiments of this latter type. Early workers (Warburg 1915) found it necessary to fertilize the eggs before the beginning of the experiment, or, after measuring the O 2 consumption of unfertilized eggs, to open the manometer vessels to effect insemination. The former method precludes any measurements during the fertilization reaction, and the latter involves a period of manipulation and consequent re-equilibration which exceeds the duration of the fertilization reaction. When, therefore, it is stated that the O 2 consumption rate increases upon fertilization or parthenogenetic activation by some 200-400%, what is usually implied is that the O 2 consumption rate measured over a considerable period of time after insemination is some 200-400% more than the rate for a similar period of time before insemination. Shearer (1922) was the first to realize the importance of measurements immediately after insemination; 1 min. After insemination he observed an increase in O 2 consumption which was not maintained at the original high level. We have been unable to confirm Shearer’s results when using a similar method (see fig. 2). In recent years further attempts have been made (e. g. Runnström 1933 b ; Brook, Druckrey and Herken 1938) to make measurements immediately after fertilization by having the sperm inside the manometer vessel before fertilization but separate from the eggs; at a given moment sperm and eggs are mixed; but in these condition, the shortest time interval measured after insemination was 10 min. (Runnström), by which time the initial phase of the fertilization reaction is over.

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.

THE effect of X-rays on the viability of cytochrome a3-deficient yeast cells, which form petite colonies, has previously been examined and compared with that of the wild type, which forms normal-sized, large colonies1–5. The reported results differ to a certain extent. Thus Moustacchi3, O'Brien5 and Gonzales and Barron2 observed an increase in radiosensitivity of petite cells, while Raut and Simpson1 and Wood4 found no such difference. This discrepancy may be due to strain differences, to the use of either naturally occurring petite mutants or of colonies produced by chemical means, such as acriflavine or gentian violet, or to the use of cells not genetically related and, therefore, not directly comparable.

An investigation was made on the effects of changes in temperature and growth rate on the post-irradiation viabil ity in E. coli. Two x-ray doses (4 and 8 kr) were given, the irradiated cells were incubated at 37 or 15 deg C, and colony counts were made after or 5 to 6 days, respectively. The temperaure did not significantly affect the number of non-irradiated cortrols, and only a small difference was found in the case of irradiated cells. The appearance of the colonies, however, differed greatly, and it was discovered that E. coli comprises two types of cells, filamentous forms forming petite colonies and single cells formr-ng large colonies. The filamentous forms were found to be more radiosensitive than single cells and to have a smaller O2 enchancement ratio. Cultures were grown from single colonies of both types to see whether the characteristics of the cells were maintained on growth at different temperatures; a clear separation of the cell types resulted. It is concluded that the formation of filaments in E. coli under unfavorable conditions complicates interpretation of irradiation effects.