98 RATE OF REPAIR OF RADIATION DAMAGE IN MICE THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD I T T t T T 100 T T T t T ence in the pattern in the peripheral blood. All of our previous experience in dogs would indicate that we could judge the effective dose biologically very well by the changes in the T)=46 DAYS: 20 oe 400r INITIAL DOSE he to report on it, so I thought I might mention “T,*2 4 HRS. z a T "1.2 HRS. 5 30] peripheral blood. Dr. Sacer. John Storer presented some very interesting data. We have a little bit of data done by a different method. I am not going T RESIDUAL INJURY (% OF INITIAL) RESIOUAL INJURY [% OF INITIAL) 50) - al . Amend BOON INITIAL COSE #—-—+ 800r INITIAL DOSE | 4 1 J | J 4 o————@ 400r INITIAL DOSE SemennO BOOK INITIAL COSE 200 300 too TIME BETWEEN DOSES (HOURS) 4 4 4 Onnmmmn® GOH INITIAL DOSE . 4 0 | v \ z | 3 1 4 4 | 3 TIME BETWEEN DOSES (HOURS) 1 6 Fisurr 5.—Slow component in repair of damage coniribuling to 100-hour lethality. Fraure 6.—Fast component in repair of damage contributing to 100-hour lethality. APPENDUM DISCUSSION After the presentation of this paper, Drs. E. P. Cronkite and D. Borg, in a private conversa~ tion with the author, suggested that all the individual mice might repair their damage by a process showing «a single characteristic halftime but that the half-times for the pepulation might vary greatly and show a Gaussian distribution. This distribution might then ex- plain the empirical fit of a line of the type R=a+b log t. This suggestion seems plausible. Further calculations are in progress to determine whether the required ranges in half-times are reasonable. J. B. Storer Dr. Cronxits. [just want to make the com- ment that following the study of the Marshallese where the changes in the blood were some- what difforent than we had anticipated we wondered whether there might be a dose rate phenomenon, and simulated the exponentially decaying field with the 4 pi cobalt radiator at the Naval Medical Research Institute by successively withdrawing slugs. We did not do an LD-50 study, but just studying the changes in the peripheral blood of the dog exposed exponentially compazed to dogs exposed at 15 r per minute there is practically no detectable differ- it now. The method is to use as a secondtest condition not a single dose LD-50, but the accumulated dose to death, giving daily dosages of about 100 ra day, such that the animals will survive approximately 30 days, accumulating 2 or 3 odd thousandroentgens. Underthese conditions, going out to about 4 months we find a persistent residue of damage on the order of about 10 percent. In other words, the groups that received the conditioning dose, usually sublethal or sometimes correctionally lethal, always could tolerate only 90 99 percent as mich as the controls for this kind of run which was about 4 months, J think that this represents no inconsistency, but a response to a different test situation which stresses the organisms in a different way. Dr. Srormr. I wouldlike to ask Dr. Cronkite over what period of time was this radiation dose delivered? Dr. Cronxrrs. It was given over identically the same period of time that the Marshallese were exposed, and starting at the same dose rate as the individuals were receiving as measured by the monitoring instruments. Actually a 48hour period. Dr. Srorzr. This would be fairly early. They were exposed to the fallout field fairly carly so that the dose rates initially were quite high. Dr. Cronxrrs. The initial dose rate as I recall was approximately 3.5 r per hour.