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Over the last 5 years realtime ultrasonography has become the most important diagnostic tool in evaluating intracranial haemorrhage and ventricular dilatation as well as structural anomalies of the newborn brain. There is excellent correlation between ultrasound findings and those of both computed tomography and autopsy.1 Unlike computerized tomography ultrasound does not use ionizing irradiation, is relatively inexpensive, can be carried out quickly and repeatedly at the cotside and involves little disturbance of the infant. With these attributes it is not surprising that it is being used both for diagnosis in infants with symptoms suggestive of periventricular haemorrhage (PVH) or hydrocephalus, and as a scanning tool for infants of birthweight less than 1500-2000 g and/or gestational age less than 33-35 weeks.

Implantation of hydrogen into Si‐SiO2 structures is seen to increase the number of E′ centers in the SiO2 induced by ionizing irradiation. Correlation of the concentration of these centers with the ESR signal due to conduction electrons in the accumulation layer indicates that these centers are related to the positive interface charge density.

Whole body exposure to 500 rad ionizing irradiation suppresses the immune system in rats. Moreover, when administered prior to chronic morphine treatment, irradiation exposure also dramatically reduces the severity of naloxone-precipitated withdrawal in morphine dependent animals. The reinstillment of 2-6 x 10(8) normal lymphoid immunocompetent cells to irradiated rats by adoptive transfer prior to chronic morphine treatment restores all withdrawal signs precipitated by naloxone injection. The data suggest that specific cellular activities or factors derived from lymphoid cells are required for the expression of opiate withdrawal, indicating that the immune system participates in the manifestation of opiate dependence.

The study of changes occurring in minerals which may occur in the rocks of geological repositories for radioactive wastes is of current concern in many countries; such changes may be caused by ionizing radiation fields produced by the radioactive wastes. One way to study these changes is to subject the minerals to controlled exposures of Y-rays and electron beams.

The effects of 3 types of ionizing radiation, γ-rays, neutrons and accelerated α-particles, were examined using the SOS Chromotest, a bacterial colorimetric assay for genotoxic agents based on the measurement of the SOS response in Escherichia coli . The SOS Chromotest appeared to be a sensitive and simple assay to detect quantitatively these radiations as well as their biological effects. The range of adsorbed doses for which induction was observed was similar for the 3 types of radiation, the minimum inducing doses being in the order of 2.5–5 Gy. We discuss the possible use of these observations to study the molecular action of radiations and to compare their genotoxic effects with those of chemicals.

Publisher Summary This chapter discusses the advances in radioembryological research in the areas of mechanisms of cell inactivation, disturbances in proliferation, long-term interference with growth or maturation, and effect modification. This chapter provides an overview of the radiation effects arising after implantation. The radiation-induced and embryotoxic responses are diverted in the same direction in various species, if noxic agents act on homologous stages of development. The model experiments with mammals are of importance for the analysis of types of damages that are diagnostically difficult or impossible to determine. This applies to the multifarious cellular response chains, which entail cytomorphological, biochemical, and functional long-term effects as a result of a transfer of effects. The experiments on animals significantly broaden the understanding of the way an original effect of damage can be transferred to subsequent stages of development and can be modified by compensatory processes to manifest itself in final form. The main interests in risk assessment focus more on developmental late effects rather than acute irradiation effects in utero.

1. 1. The influence of temperature on the incorporation of [32P]phosphate and [14C]acetate into gill lipids in vivo depends also on environmental salinity. 2. 2. Ionizing irradiation (1000 r) results in a relatively enhanced incorporation of [32P]phosphate into phosphatidyl choline and of [14C]acetate into triglycerides and wax esters in vivo. 3. 3. When gill tissue is removed from the animal and incubated in vitro, a pronounced dependence of lipid metabolism on previous environmental salinity is not observed.

Ionizing irradiation has received considerable attention as an experimental means of accelerating biological aging since it can decrease the median life span, particularly in younger age groups (Sikov & Mahlum, 1969; Samorajski, et al, 1970). There is a decreasing life shortening with increasing age at exposure (Lindop & Rotblat, 1962; Kohn & Guttman, 1963; Jones & Kimeldorf, 1964). In extreme old age, life expectancy may actually increase after low doses of whole body irradiation (Yuhas, 1971).

✓ Earlier reports have suggested that low-dose ionizing irradiation might be involved in induction of intracranial meningiomas. One of the problems in evaluating irradiation-induced neoplasms is the belief that these tumors have no distinguishing features to indicate their etiology. In an attempt to identify such features in meningiomas following irradiation, a group of 42 post-irradiation meningiomas (PIM's) has been compared with a group of 84 non-PIM control meningiomas. These 42 PIM's included all the intracranial meningiomas diagnosed at the Hadassah University Hospital during the years 1952 to 1981 in individuals treated in childhood with low-dose x-ray therapy for tinea capitis. Although the individual PIM does not seem to differ from a “spontaneous” meningioma, this study indicates that PIM's as a group have distinct characteristics, namely, their location at the site of maximal irradiation, and features suggesting rapid growth and aggressive biological behavior. There was a significantly higher number of calvarial tumors (p < 0.001), a high proportion of multiple meningiomas, a higher recurrence rate following apparent complete excision (p < 0.02), and an increased number of histologically malignant meningiomas (p < 0.01). The demonstration of features that distinguish PIM's from meningiomas of other etiology supports the suggestion that low-dose ionizing irradiation was involved in the pathogenesis of these tumors.

Rats were trained to perform one of three tasks in which responses on a lever delayed the onset of footshock for 20 sec. One task provided a warning tone beginning 15 sec after the last response on the lever and lasting for 5 sec just prior to the presentation of a shock (fixed-interval signalled avoidance), while a second task provided no external cues (unsignalled avoidance). The third task was similar to the fixed-interval signalled avoidance task, except that the warning tone preceding shock began at varying intervals after the last response on the lever (variable-interval signalled avoidance). Animals trained on the signalled avoidance paradigms received fewer shocks than those on the unsignalled avoidance paradigm. After 10 krads of gamma radiation, animals performing on either task with cues were less able to avoid shock, although they recovered somewhat over a 90-min period. The animals not provided cues also experienced more shocks during the first 10 min after irradiation but were relatively less affected in performing the task. Response rates on the bar and the patterns of responding on these tasks were not significantly different after irradiation, except that animals responded after the onset of shock more often after irradiation than before. These results suggest that rats will continue to effectively use task related cues after irradiation, but that the relative degree of behavioral decrement may depend on the initial level of performance or possibly the complexity of the task.

Dose response curves were obtained from Chinese hamster cells irradiated in different growth stages and under different nutritional conditions with either X-ray or ultraviolet light. All X-ray survival curves were asymptotically exponential, while the shape of the UV-curves was bi-phasic. Survival of X-irradiated cells was much less influenced by cultural factors than survival of cells exposed to UV. Recovery of cells from potentially lethal damage had a T1/2 of 1–2 h after exposure to the ionizing irradiation, while it took considerably longer to recover 50% of the UV induced damage. Similarly “fixation” of X-ray damage was relatively rapid (T1/2 ⋍ 30 min) compared to “fixation” of UV damage (T1/2 ⋍ 3.5 h). Finally, exposure of cells to 43°C for 1 h immediately after X-irradiation resulted in synergistic cell killing and subsequent complete inhibition of recovery from potentially lethal damage. On the other hand similar heat treatment of UV-exposed cells resulted only in additive cell killing and did not inhibit recovery.

Expansion of crystals resulting from X irradiation was studied in the case of a peptide, N-acetyl-D, L-alanine. This expansion was discovered by examining several irradiated organic solids for possible expansion, which was suggested by the recent observation of crystal imperfections in another peptide. The expansion, which occurred anisotropically along the c axis, was found to depend on dose, the maximum being as large as 20% when assisted by heat treatment.

Etude effectuee autour de la centrale nucleaire de Sellafield qui repond dans la mer et dans l'atmosphere de l'iode 129 et de l'iode 131 depuis 1960 environ. La dosimetrie corps entier est correlee a la proximite de la centrale, mais il n'est pas demontre d'augmentation significative des taux de cancer de la thyroide

Publisher Summary Immunological tissue damage is a common cause of acute and chronic disease in man. Immune reactions also hinder transplantation of bone marrow or solid organs between histoincompatible individuals. As immunological disease and transplantation reactions often result in severe, occasionally life-threatening conditions, it is important to provide immunosuppressive therapy to prevent or decrease the tissue damage. Despite the fact that such treatment has been used for over 30 years, knowledge about the mode of function of immunosuppressive drugs and the risks of long-term treatment is incomplete. Clear indications for immunosuppressive therapy are present only in transplant patients and in a few immunological diseases. Ionizing irradiation and immunosuppressive agents are limited in their applicability because of their nonspecific effects on the immune system and other organs introducing the risk of severe side effects. Despite its deficiencies, nonspecific immunosuppression is an important complement to other treatment and, in many instances, the only efficient therapy the patient can be offered. The ideal immunosuppressive treatment is directed only against the immunological reaction causing the disease. Such immunologically specific immunosuppression has so far only been successful in Rh prophylaxis.

The effect of ionizing irradiation on the barrier function of the rabbit popliteal lymph node was studied using the V2 rabbit carcinoma. The popliteal lymph node acted as an effective barrier to viable V2 tumor cells for 2–3 weeks. Three weeks after tumor infusion, distant tumor growth was significantly increased in rabbits receiving 1000 rad and 3000 rad to the popliteal node. Six weeks after tumor infusion, all three groups had similar incidences of distant tumor growth. The number of tumor takes was similar in all groups. However, the tumor mass in the irradiated popliteal node was markedly smaller than the tumor mass in the control node at 3 weeks and 6 weeks. The earlier presence of tumor in the pelvic nodes of the irradiated rabbit may be dependent on the following factors: (a) irradiation decreased the barrier function of the lymph node, or (b) the irradiated lymph node was unable to retain growing cancer cells for the same length of time as the normal node. This effect of irradiation on the lymph node may be only a transient influence.

Synergistic effects of prolonged heat exposure and whole body irradiation with ionizing radiation on survival time in hamsters

The activity of two dehydrogenase systems of the pentose cycle (glucose-6-phosphate-dependent and 6-phosphogluconate-dependent) as well as the lactate-dependent dehydrogenase system was studied in homogenates of four regions of the adult male rat gastrointestinal tract following 1540-rad whole- body x irradiation (WBR), or 1400-rad mixed gamma-neutron radiation. Microchemical assays using a tetrazolium salt (INT) were done at intervals after irradiation (10-20 minutes, 1, 2, 3 days). By 1 day postirradiation there was a significant fall in activity in both pentose cycle systems as well as in the lactate-dependent system in the stomach. For the most part, the fall in activity did not occur in the intestinal regions until the 2nd day. This depression became most prominent by 3 days for the regions studied. The lactate-dependent dehydrogenase system activity of three regions of the gastrointestinal tract was more drastically affected by the radiations delivered than was that of the pentose cycle systems. The fourth region (distal end of the large intestine) was not consistent with the others, in its response. It seems from this study that the dehydrogenase systems which are intramitochondrial in location showed a greater reduction in activity than did those which are extramitochondrial.

Intrafusal (IF) fibers in leg muscles of the rat increase in number from two at birth, to three at day 3, and to the adult four fibers by the sixth day. The question of whether this multiplication and the attainment of the adult complement of fiber nuclei involves mitotic division was approached by subjecting one leg of rat pups to x-irradiation in single doses up to 1200 R, and comparing treated and control plantaris muscles on complete histological serial sections taken at 1 month of age. The mitotic process is particularly susceptible to ionizing irradiation and since periods for multiplication of IF fibers are fairly precisely scheduled, irradiation even in a single dose might be expected to disrupt future development. However, no effects were detected on number of spindles per muscle, on spindle complement of nuclear bag and chain fibers, or configuration of the nucleated region. Irradiation of gravid rats in the latter half of pregnancy with a single dose that was near lethal for the fetuses was also without obvious effect. Muscle spindles in several rat pups given single doses of colchicine were unaffected. Failure of these procedures to disturb spindle development supports the likelihood that the multiplication of IF fibers and allotment of nuclei that takes place in late natal and early postnatal periods is an amitotic process.

The decrease of NADH following ionizing irradiation was investigated over a concentration range from 10−3 to 5 x 10−8 M. The nonexponential function of the curve was discussed. TheG-values were calculated for different starting concentrations. The results were compared with theG-values for NADH following irradiation under enzymatic equilibrium conditions and with somein vivo investigations reported in the literature.

Summary and ConclusionsPituitary tumors were induced in mice by a single exposure to ionizing irradiation. The greatest incidence occurred among mice exposed to doses of gamma radiation somewhat below the LD50. These Tumors were about four times more frequent among females than among males. Neutrons appear more efficient in inducing these neoplasms than gamma rays, and the data suggest that doses as low as 40- 70 rern may induce such tumors. The period of latency of these neoplasms is very long, the maximum incidence being at 17-25 months postirradiation.

The potentiation of radiation damage by hadacidin in proliferating E. coli has been investigated. Apparently this effect of hadacidin may be due to an effect in previously described mechanisms of inhibition by hadacidin: (a) inhibition of adenylosuccinate synthetase and (b) undefined inhibition of energy production. E. coli cells grown in the presence of adenylic acid, adenine, oxalacetic acid, or anthranilic acid for 4 hours before exposure to radiation are insensitive to the hadacidin radiation effect.

A series of experiments was performed to determine whether agents which alter the effects of ultraviolet light might favorably influence the survival rate after total-body exposure to ionizing irradiation. Antimalarials, psoralen, benzophenones, and a benzotriazole were administered in the diet to albino mice before irradiation. The results were inconclusive but suggested that certain agents of this type may be capable of providing some degree of protection and that further experimentation and evaluation would be justified. The need for research on practical methods for protecting man from the effects of excessive radiation is emphasized. To date the sulfhydryl compounds have shown the most promise for this purpose.

The variable results obtained in the treatment of malignant melanoma by radiotherapy alone or combined with surgery, have suggested more detailed studies on the radiosensitivity of this tumour. Data on this problem are contradictory and rather scarce because: 1. Differences in histological structure and radiobiological reactions of malignant melanomas considerably restrict the comparison of data from different patients. 2. These differences also render difficult comparison of changes in the irradiated tumour and non-irradiated metastases, and vice versa, in one and the same patient. 3. A systematic histological examination of the primary tumour in a patient cannot be undertaken because of the contraindication of biopsy prior to, during and following irradiation. 4. Clinical evaluation only of the effect of ionizing irradiation on malignant melanoma is quite insufficient. 5. Data on the radiosensitivity of malignant melanoma in animals cannot be related to malignant melanoma in man because of the biological differences of these tumours.

Extensive prior investigations have revealed that certain mammalian lymphocytes are extraordinarily susceptible to irradiation [1, 2], Other lymphoid cells show considerably greater resistance to destructive effects both of ionizing irradiation and of certain alkylating agents [3, 4, 5, 6, 7]. Among the cells known to be highly susceptible to irradiation are mammalian small lymphocytes, including lymphocytes residing within the thymus.

Biophysical modeling of radiation-induced DNA damage shows that significant yields of clustered DNA damage are formed after energy deposition by a single radiation track. To date, the majority of studies on radiation-induced DNA damage in cells have concentrated on determination of the yields of single- and double-strand breaks (DSBs), the latter representing one type of clustered DNA damage. It was recognized, however, that clustered DNA damage, which does not contain a DSB, might contain a combination of DNA base lesions and single-strand breaks in proximity. This mini-review discusses some of the recent experimental data confirming the induction of non-DSB, clustered DNA damage by radiation.

The radiation sterilization standards EN 552 and ISO 11137 require that dose mapping in real or simulated product be carried in connection with the process qualification. This paper reviews the recommendations given in the standards and discusses the difficulties and limitations of practical dose mapping. The paper further gives recommendations for effective dose mapping including traceable dosimetry, documented procedures for placement of dosimeters, and evaluation of measurement uncertainties.

The radiation-induced effects at dose rate of 0.35 Gy/min (in vivo) and of ultra-low doses (in vitro) on the cell membranes structural state were shown. The modifications of the membrane protein and lipid components and their dynamic state were revealed at experimental irradiation conditions by fluorescent probe analysis. The principal component analysis of the research data indicates the dose-dependent decrease of plasma membrane structural orderliness of the small intestine enterocytes with the increase of the ionizing irradiation acute dose of 0.5, 1.0, 2.0, 3.0 Gy at dose rate of 0.35 Gy/min. The complex response of the biological structure – the erythrocytes plasma membrane, on the ionizing radiation action at ultra-low doses that occurred through macromolecular structural rearrangements was also demonstrated. The features of the structural rearrangement of the cellular membranes depending on the ionizing radiation dose (dose rate) are found out.

To investigate the response of the spinal cord of experimental animals to homogeneous irradiation, the main purpose being to propose a new version of the Critical Volume Normal Tissue Complication Probability (NTCP) model, incorporating spatial correlation between damaged functional subunits (FSU).The standard Critical Volume NTCP model and its modified version, the Contiguous Damage model promoted here, are described in mathematical terms. Also, a fiber-like structure of the spinal cord is considered, which is a more complex structure than the standard Critical Volume NTCP model assumes. It is demonstrated that the Contiguous Damage model predicts different responses to two-segment irradiation and to single-segment irradiation to the same combined length as observed in experiments on rats, a result that cannot be described by the standard Critical Volume NTCP model.Both the Critical Volume model and the Contiguous Damage model, are fitted to two sets of canine spinal cord radiation data corresponding to two different fractionation regimes of irradiation. Whole-organ irradiation as well as partial irradiation to different lengths are considered, allowing the investigation of dose-volume effects. Formal goodness-of-fit investigation shows that both models fit the canine spinal cord data equally well.

Radiotherapy applies ionizing irradiation to selected areas of the body with the scope of destroying cancer cells, either as part of curative therapies to remove a primary malignant tumor and to prevent tumor recurrence after surgery, or as part of palliative measures to avoid local advancement of bone and brain metastases. Intriguingly, radiotherapy does not only have local effects but may lead to the delayed regression of distant non-irradiated lesions. Most likely, these “abscopal” effects are mediated by the immune system.

Radiotherapy (RT) with ionizing irradiation is commonly used to locally attack tumors. It induces a stop of cancer cell proliferation and finally leads to tumor cell death. During the last years it has become more and more evident that besides a timely and locally restricted radiation-induced immune suppression, a specific immune activation against the tumor and its metastases is achievable by rendering the tumor cells visible for immune attack. The immune system is involved in tumor control and we here outline how RT induces anti-inflammation when applied in low doses and contributes in higher doses to the induction of anti-tumor immunity. We especially focus on how local irradiation induces abscopal effects. The latter are partly mediated by a systemic activation of the immune system against the individual tumor cells. Dendritic cells are the key players in the initiation and regulation of adaptive anti-tumor immune responses. They have to take up tumor antigens and consecutively present tumor peptides in the presence of appropriate co-stimulation. We review how combinations of RT with further immune stimulators such as AnnexinA5 and hyperthermia foster the dendritic cell-mediated induction of anti-tumor immune responses and present reasonable combination schemes of standard tumor therapies with immune therapies. It can be concluded that RT leads to targeted killing of the tumor cells and additionally induces non-targeted systemic immune effects. Multimodal tumor treatments should therefore tend to induce immunogenic tumor cell death forms within a tumor microenvironment that stimulates immune cells.

Xenogeneic tissue devitalization is one of the creating methods of the tissuereplacing the biocompatible cell-free shells for the regenerative surgery. The work describes the possibility of applying the complex approach based on the continuous usage of cryo and radioactive (electron irradiation exposure) biological tissue damage effects. The pre-implant treatment provides sterilization and a possibility for the low temperature preservation of xenografts. After the transplantation such a cell-free xenoscaffold can be gradually replaced with the autogenic extracellular matrix from the recipient’s cells and forms a stable long-term structure of the biological prosthesis. Fibrous pericardium (FP) and aortic valve leaflets (AVLs) were extracted from the mature pig. The prepared tissues were rinsed with the sterile normal saline solution and frozen down to the liquid-nitrogen temperature. After one time placing on water-bath (37°C) they were exposed to electron irradiation within dosage range of 25-30 kGray and submerged into the liquid nitrogen vapors. After influence of low temperature and ionizing radiation, tissue morphological structure was assessed using the optical microscopy. Deformations, i.e. longitudinal and transverse monoaxial strength were performed to calculate the physical and mechanical properties of FP and AVLs. Such a devitalization method of the FP and AVLs causes significant destructive changes in cell elements, however the spatial arrangement and structural integrity of the connective tissue fiber are preserved. Joint impact of low temperatures and ionizing radiation gives the synergetic effect, increasing the strength and elastic tissue properties. Freezing down to –196 °C and electron irradiation initiate formation of the intra- and intermolecular transverse cross-linking due to the binding activity of fibrous proteins. It leads to a more dense arrangement of the collagen fiber, adds strength to the implant and provides the structural tissue stabilization. The authors believe that during the remodeling in the recipient organism, the biomaterial structure modified in such a manner can successfully prevent physiological tension.

In this paper an algorithm for the investigation of routine curves in thermoluminescence personal dosimetry is presented. In rare cases, the luminescence glow curves do not exhibit the expected form. They have an abnormal shape as a result of, for example, external contamination, hardware problems, and poor heat transfer. So, glow curves from a monthly exposure period are compared with regular glow curves. Each curve is divided into four regions of interest (ROIs) and the relationships between the different ROIs are analysed. There are few criteria combining all four ROIs, which are necessary to distinguish between normal and abnormal glow curves. For that, the numerical value and the channel of the curves maximum also need to he considered. In most cases an additional set of criteria permits the identification of the ROI in which the irregularity occurs.

Density, energy distribution and capture cross sections of the surface states on n-type Si are evaluated, before and after ionizing irradiation ( 60 Co). The existence of surface states is intimately connected with the non-stoichiometry of SiO 2 near the interface silicon/insulator.

A case of primary reticuloendotheliosis of the lung diagnosed clinically, radiologically, and by lung biopsy is presented. The patient responded well to ionizing irradiation.

Pregnant Wistar rats were exposed to either microwave-induced hyperthermia or gamma radiation or a combination of both. In microwave-induced hyperthermia, a core temperature of 42 degrees C was slightly teratogenic and a core temperature greater than or equal to 43 degrees C was highly teratogenic. Gamma radiation at 40 cGy was subteratogenic, while a dose of 75 cGy was highly teratogenic. A combination of microwave-induced hyperthermia up to 42 degrees C with 40 cGy of gamma radiation was highly teratogenic, indicating a mutual potentiation of the embryotoxic action of these two teratogens.

The oxygen enhancement ratio (OER) of proliferating and nonproliferating cells grown in vitro was measured using accelerated fractionated regimens. Irradiations were performed either twice daily or three times per day, with a minimum of 6 h between the consecutive fractions. The dose delivered was 2.3 Gy per fraction. Two significant observations were made: (i) the OER of accelerated fractionation regimens for proliferating cells is lower than that obtained from single-exposure experiments at 2.3 Gy (approximately 1.4 vs 2.4, respectively), while for nonproliferating cells it is approximately the same (2.3); (ii) the fractionated regimen does not spare proliferating cells irradiated under hypoxic conditions, and thus the fractionated survival curve lies below the single-exposure curve. For cells irradiated under aerobic conditions or for nonproliferating cells, irradiated under either hypoxic or aerobic conditions, the fractionated survival curve lies above the single-exposure curves as expected.

ROTI ROTI, J. L., AND HENLE, K. J. Comparison of Two Mathematical Models for Describing Heat-Induced Cell Killing. Radiat. Res. 81, 374-383 (1980). A computer-based minimization algorithm is utilized to obtain the optimum "fits" of two models to hyperthermic cell killing data. The models chosen are the multitarget, single-hit equation, which is in general use, and the linear-quadratic equation, which has been applied to cell killing by ionizing irradiation but not to heat-induced cell killing. The linear-quadratic equation fits hyperthermic cell killing data as well as the multitarget, single-hit equation. Both parameters of the linear-quadratic equation obey the Arrhenius law, whereas only one of the two parameters of the multitarget, single-hit equation obeys the Arrhenius law. Thus the linear-quadratic function can completely define cell killing as a function of both time and temperature. In addition, the linear-quadratic model will provide a simplified approach to the study of the synergism between heat and X irradiation.

The effect of ionizing irradiation on the embryo and fetus has been somewhat neglected in radiobiologic research. In the past decade, however, several works have been published which have illustrated certain aspects of the problem. These studies, which are concerned mainly with the effects of doses of more than 100 R, have, in the majority of cases, had an embryological object (1, 2). From a clinical point of view and on account of the greatly increasing employment of ionizing irradiation, it would be of interest, particularly in diagnostic radiology, to illustrate in more detail the problems concerning the possible injurious effects of small irradiation doses on the fetus. It is of particular interest to elucidate the effect of irradiation when this is applied during a period during which the fetus is particularly sensitive. In women this period is presumed to extend from the second to the eighth weeks of pregnancy. From a practical point of view this period is also important, as women referred during this period for radiological diagnostic investigation of the pelvic regions are, as a rule, unaware of the existence of pregnancy, particularly if the menstruation is already somewhat irregular. The present investigation is an attempt, on animal material, to illustrate in more detail a few of the problems that occur when ionizing irradiation is applied in small doses at an early and sensitive stage of embryonic life. Lindop and Rotblat (3) irradiated mice 3 weeks old with 50 R and found, as might be anticipated, the weight curve lower than the normal curve. However, when the animals had passed the age of 14 weeks, the weight curve of the irradiated group tended to a higher level compared with the controls. This peculiar phenomenon is not discussed further in their work. A similar result after fetal exposure was published by Nash and Gowen (4).

Investigations show that the free radicals obtained at room temperature in the amino acids are generally not the same as those found when the sample is irradiated at the much lower temperature of liquid nitrogen, 77 deg K. However, when the sample is irradiated at the lower temperature and allowed to warm to room temperature, the radical obtained is usually the same as that produced by irradiation at room temperature. lt thus appears that the free radicals observed at room temperature are generally not the primary ones produced by the ionizing irradiation, but are secondary free radicals produced by molecular motions after the primary event of ionization. (auth)