117 cartilages from strain H mice were similarly affected, but only after 7200 Rads at 14 days. We did not ob- serve the postirradiation recoveryclones of cells in cartilage as did Sams") and Kember,® 1 but this was probably due to the advanced age of the mice at the time of irradiation, as well as to the low bone dose. The data plotted in Figure 91 (strain HW) suggested that there might be a concomitant increase in the DNA synthetic indices and thicknesses of the growth carti220 57 mice,§ — hairless f ch four? ace beta ic, 90—A photomicrograph of a longitudinal section from ch and the tibia of an HB strain C57 mouse three days after partial n of ce-— whole-body irradiation with 7200 Rads. The proximal epi- a—s 5000r x CARTILAGE PLATE THICKNESS (p) Jong10sa or these 2!Oq200 190 180 170 1601 150 140 130 120 110 100 30: id e sheets, t alumi-f ‘8 sealed end andf adiation 80 poe phvseal eartilage is perforated by a blood vessel to unite the epiphyseal and diaphyseal marrow spaces. Hematoxylin and cosmn. 250%, The hind legs of the mice were recovered at autopsy. They were fixed in 10% neutral formalin, decalcified ra vena 10% EDTA, embedded in paraffin, and sectioned > 11 andg sigitudinally at 5 yw. The sections were stained with from i-— hematoxylin and eosin. : studies f ns indi-§ RESULTS AND DISCUSSION ‘ich de-f The histologic picture of the long bones from mice of | within} strains H, HW, and HB suggests that they were not int. Thef undergoing rapid growth in length. This would be con6-hr ir- | sistent with the fact that the mice were 4 months old QO ‘ted un-§ “00 Rads and 7200 Rads, and the amount of damage ie orderk observed and the pattern of healing also seemed to be ‘stimate 2 do not# contact e entirel inimals, F ind un-— were alll irradia-§ dcpendent upon the strain. The histologic damage observed in the cartilages of hones from the mice involved cartilage, marrow, and Vascular anomalies similar to those previously de“ribed for rats.) *) Epiphyseal-diaphyseal fusion ‘igure 90) occurred 1-3 days after irradiation with ‘00 or 7200 Rads in strains HB and HWmice and “as present in strain HB mice as late as 120 days. The J OTT ® 10 20 30 40 50 60 70 80 120 130 140150 160 170 DAYS POSTIRRADIATION Fic. 91-——A plot of the thickness of the proximal tibial epiphyseal cartilages of strain HW C57 mice vs. time after partial whole-bodyirradiation with 5000 and 7200 Rads, The maximum reduction in cartilage thickness which occurred during the second week was interrupted by an earlier abortive attempt at recovery. The time periods required to thin the cartilages and to achieve partial recovery on the twentieth day were much longer than in the other strains (compare with Figures 92 and 93). TABLE 55. Days to AcHIEVE SUPPRESSION AND RECOVERY FROM [IRRADIATION DAMAGE IN THE BONES OF THREE STRAINS oF C57 MiIcE Tespec-# when the experiment began. There were some differie cellu-§ ‘ices In the magnitude of the response of the bones to cavities Jrtial-body beta irradiation at surface doses of x 7200r Total-body C57 strain surface dose,| Rads Days postDays postirradiation tojirradiation to} maximum partial Days from maximum reduction in| recovery of piate thickness plate thickness recovery cartilage cartilage injury to partial If 5000 7200 5 3 9 9 4 6 HW 5000 7200 14 9 20 20 6 11 HB 5000 7200 5 5 9 9 4 4