1. The hemorrhagic syndrome following exposure of rats to 400 r x-irradiation was studied. A blood coagulation defect was found in the irradiated animals.

2. This coagulation defect is quantitatively reflected by an increased heparin clotting time, and by alterations in the blood resistance measurements: lowered resistance, increased time until the beginning of clot retraction, and decreased clot retraction rate.

3. The decreased level of platelets in blood following exposure of the rat to radiation appears to be a major factor in defective clotting.

4. The post-irradiation hemorrhage appears to be correlated with the defective blood coagulation. At sixteen days after irradiation the degree of internal hemorrhage has reached its maximum value. Maximum deviations are also noted in clot retraction rate, time until inception of clot retraction, platelet level and heparin clotting time.

5. The heparin clotting time measurements and the electrical resistance measurements presented in this paper provide quantitative baselines for the clotting reactions before and after 400 r x-irradiation. Such eriteria make possible the evaluation of various therapeutic agents in terms of their effect on coagulation.

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© 1952 by American Society of Hematology, Inc.
1952
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