4.4 Sr®® in Sheep Bone The Sr®° in calcium ratio in the bones of yearling sheep at stations A to G are shown in Table 2, and the normalized S.U. values are plotted against soil calcium in Fig. 5. Independent estimations by different laboratories on mixed ash samples show reasonable agreement, but there is an unknown variation between animals from the sameflock. The range of results for sheep from different areas in 1956 is as follows:* No. Range (S.U.} Median (S.U.) Lowland sheep 7 7.8 to 15.6 14 Hill sheep 6 24 to 160 57 The hills grazed by sheep in Britain are generally areas of high rainfall. The soil is uncultivated, peaty and of low calcium status and there is low yield of vegetation. Any or all these factors may tend to enhance the uptake of Sr**. The lowland farms generally have the opposite conditions. It is not possible to deduce from the present results the relative importance of these factors, but it is clear, from Fig. 5 that variation in the total fallout of Sr®* is not the sole cause. The bones of hill sheep contain more Sr*® per unit fallout than those of lowland sheep. 4.5 Ratio of Strontium to Calcium in Herbage and Sheep Bone In Table 4 the Sr /Ca and Sr®’/Ca ratios in grass and sheep bone at stations A to G are compared. The estimations of stable Sr were made by the Spectrographic Section, Chemistry Division (Woolwich Outstation) using methods which will be reported separately. The discrimination against Sr in passage from grass to bone is shown with both stable and radioactive Sr. Following Comar et al. (1956, 1957), the “Observed Ratio” (OR) is defined as: OR _ Sr/Ca in bone bone~gras8 sy /Ca in grass The OR for the sheep-bone/grass comparison varies between 0.15 and 0.31 for stable Sr, and between 0.09 and 0.42 for Sr°", The mean of the OR’s at the various stations is 0.24 (stable) and 0.23 (radioactive). These values are in excellent agreement with results reported elsewhere with various animal species (Comaret al., 1957). Table 4—STRONTIUM/CALCIUM RATIOS IN GRASS AND SHEEP BONE Stable Sr, pe/g Ca Station Sr™ | e/g Ca eee, a Bone Bone Grass OR Grass OR A 730 5000 0.15 160 1750 0.09 B 470 1500 0.31 41 123 0.33 D E 470 650 1700 2800 0.28 0.23 53 71 125 625 0.42 0.14 F 520 2500 0.21 12.8 64 0.20 G 930 3400 0.27 8.7 41 0.21 Average 0.24 0.23 9 RADIOSTRONTIUM IN MILK A series of samples of spray dried skimmed milk from a factory at Frome, Somersett have been analyzed, some in New York (by the kindness of Dr. J. H. Harley) and some at Wool*Some additional bones from animals killed in the early part of 1956, reported by Bryant et al. (1956) have been included. *The location was wrongly referred to as Yeovill by Bryant et al., 1956. 217