1. The hemorrhagic syndrome of acute radiation illness in goats and swine has been described. This syndrome is predominantly a result of a combination of "increased vascular fragility" and thrombopenia. Infrequently, a blood coagulalation defect characterized by a prolonged clotting time due to a circulating anticoagulant with heparin-like properties appears, thus confirming under some conditions in goats and swine the work of Allen on "heparinemia" in irradiated dogs.
2. The prolonged blood coagulation time appeared only in fatally irradiated goats and swine.
3. Evidence was presented suggesting that serum fibrinolysins may have been activated.
4. It is concluded on the basis of this work and that of others that a hemorrhagic syndrome can develop in irradiated dogs, goats, swine, rats, chickens and guinea pigs without the appearance of a prolonged clotting time and without a detectible "heparinemia." The biologically most universal phenomena observed in the hemorrhagic syndrome of radiation illness appear to be: (a) increased vascular fragility, (b) thrombopenia, and (c) ulcerations.
ACKNOWLEDGMENTS The author is highly indebted to Captain R. H. Draeger, MC, USN, officer in charge; Captain Shields Warren, MC, USNR, executive officer; Commander, John L. Tullis, MC, USN, pathologist, Naval Medical Research Section Operation Crossroads for guidance and assistance in all phases of this work, and to Dr. George V. LeRoy for having kindly edited this paper and given valuable suggestions.