Acta Morphologica 13. Supplementum (1965)
Proceedings of the annual meeting of Hungarian Pathologists and Anatomists. Kecskemét, 1964
tested and confirmed by experiments on various species, including man. The pertaining tests fall into two groups: firstly radiotoxicological observations of the embryonal organism, discussed here so far as they are significant in revealing the mechanism of action; secondly experiments to test the teratogenicity of ionizing rays, with reference to the morphology, in some measure to the vital functions of the monster they bring about, and to the teratogenic mechanism. A general shortcoming of the relevant literature is that it fails to indicate whether air doses or absorbed doses have been used and at what degree of homogeneity the rays have been applied. Right, in my view, is to measure the absorbed dose by thermoluminescent methods. The radiotoxicologic cardinal question sounds like this: what is the minimum total dose and the minimum dose rate that w ill kill the embryo within 20 hours (acute lethal dose, LD) and within 10 to 15 days (delayed lethal dose), respectively? Answers in the literature are fairly agreeing. Karnofsky [2], studying X-rayed chicken embryos 3, 4, 5 and 13 days of age, found the 20 hour LD50 to be 2000, 1800, 1450 and 750 r. This agrees on extrapolation with Boland’s results [3] who found that the 6 hours LD50 for 3, 4 and 5-days chicken embryos is 946, 905 and 872 r, respectively. Fully confirming Karnofsky’s results were those of Goldman et al. [4], while slightly lower values were obtained by Goffi (Fig. 1). Whatever the results of these different experiments, they all testify to the fact that the very young embryo is resistant to acute lethal radiation and that the resistance gradually decreases in the course of embryonal life, until it settles at a certain level. The delayed lethal ray effect is not amenable to this test and, unlike the acute effect, it is independent of the dose rate. With Dixon’s words [6] as the physiological life reaches more complicated stages, the embryo becomes more vulnerable. The simpler forms of life generally go with a higher degree of resistance to radiation. Russel’s studies [7, 8, 9] have furnished the fullest comparative data for the teratogenic effect of ionizing rays. He found that the embryo’s response to radiation depends primarily on its age. As to the kind of reaction, there are three stages during intrauterine development (Fig. 2): the preimplantation, the organogenetic and the foetal phase. Irradiation before implantation led mostly prenatal death, very rarely to abnormalities of development. When exposure occured during the organogenetic phase, then abnormalities were frequent and prenatal death was rare. Histology ascertained a breaking of the chromosomes, with formation of micronuclei, to which most of the effect can be ascribed. The sooner before implantation we expose the cells to radiation, the greater part of them will suffer lethal chromosome injury, leaving no time for an abnormality to develop. The comparative rarity of developmental abnormalities explains itself by the regulating capacity of the totipotent blastodermal cells in the period closely preceding implantation, a capacity