LETHAL EFFECT AND VISIBLE IRRADIATION DAMAGE

¹ From the Radiobiology Laboratory, Roswell Park Memorial Institute (New York State Department of Health), Buffalo, New York

The present study utilized 650 axolotls (Siredon mexicanum), 12 days after hatching. In one series of experiments involving 500 animals from one spawning, nine groups of 50 animals each received totalbody irradiation with 200, 300, 400, 600, 800, 1,000, 1,500, 2,000, and 3,000 r, respectively. In another series of experiments involving 150 animals from another spawning, two groups of 50 animals each received 100 and 200 r, respectively. In each series of experiments, the remaining 50 animals served as untreated controls.

1. All doses from 200 r up very definitely suppressed growth.

2. The response of the skin epithelium to irradiation, even with a dose as large as 3,000 r, was highly diverse, and at most only partial. Not a single animal with totally damaged skin epithelium could be found, but the skin epithelium was completely normal in some instances even after 3,000 r. In some areas of the skin epithelium of irradiated animals, giant cells developed and the simple squamous epithelium was transformed into stratified columnar epithelium.

3. Loose connective tissue, muscle, skeletal tissues, and neural tissue were completely normal in all irradiated animals.

4. Likewise, the intestinal track, the liver, the olfactory chambers, and the eyes were completely normal in all irradiated animals.

5. Damage to the spleen in irradiated animals was obvious. The organ was greatly reduced in size, and the number of cells in it was also greatly reduced. The presence of pigment cells and large cells with granulated cytoplasm was characteristic of the degenerated spleen.

6. The number and size of blood vessels and the number of blood cells was obviously reduced.

7. Mitotic activity was greatly suppressed.

8. Paradoxically, visible changes in the tissues were extremely limited, despite the decidedly lethal effect of even small doses of radiation. Presumably the reason why the animals died was that irradiation was followed by complete degeneration of the spleen. It seems that the spleen is the only blood-forming organ that these animals have at this early stage in their development, and hence the immediate cause of death for the irradiated animals was probably exhaustion of the blood as a result of disappearance of the blood cells.

9. Even such radiosensitive organs as the olfactory chambers and the eyes were normal in irradiated animals. Paradoxically, the regions without directly observable damage appeared normal because the animals died as quickly as they did, before the latent periods for these particular tissues and organs were completed. The latent period for each region of an organism is independent of the general condition of the organism. Even if the organism is sick from the effects of radiation, even if it is dying from those effects, a tissue whose latent period has not been completed will appear normal.

10. It must be recognized that some variation in the length of the latent period is possible for animals of the same species and the same age. Likewise, variation in sensitivity to radiation also occurs in animals of the same species and the same age. Differences of several days in the length of the latent period can be observed even in animals of the same age.

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