D. G. BROWN 
877 
100 
90 
80 
70 
^ 60 
t 50 
< 
£ 40 
o 
30 
20 
10 
SWINE- Coy- RADIATION 
T 1 1 r 1- 
50rads/min 
lOrads/min 
I rad/min 
200 
300 
400 500 600 
DOSE (RADS ) 
700 
800 
900 
Figure 1. — Thirty-day mortality curves for swine exposed to *°Co gamma radiation with 95% confidence intervals 
for 50% mortality. 
were 710, 435 and 360 rads, respectively (Fig- 
ure 1). The relative effectiveness of 10 and 50 
rads per minute in causing 30-day mortality was 
1.63 and 1.97, respectively, v^ith 1 rad per min- 
ute having been arbitrarily assigned the value 
of 1. Although dose rate significantly affected 
the dose-mortality curves, it did not affect sur- 
vival time or the general clinical syndrome. 
The ability of an animal to recover from 
radiation injury seemingly is an important fac- 
tor in the over-all response of an animal to ir- 
radiation. Swine appear to have the highest 
rate of recovery among the large animal spe- 
cies.i* In studies where fractionated doses of 
gamma radiation were used (Table III), the 
apparent rate of recovery from radiation injury 
based on survival time seems unrealistic when 
compared with other large animal species, yet 
the data available are sufficient to be convinc- 
ing. Recovery rate appears to vary among the 
swine which is indicated in the mortality 
pattern from daily dose fractionation (Figure 
2). 
Recovery from radiation injury measured by 
the split-dose technique indicated that Duroc 
swine 8 to 9 months old had recovered from 
51% of the initial injury at 3 days after expo- 
sure and from 65%, at 7 days. At 20 days after 
