wich and Harwell. The results are shown in Fig. 6 together with the cumulative Sr*” fallout in rain at Milford Haven, reported by Stewart et al. (1956). 7 CUMULATIVE TOTAL 5°99 FALLOUT 6 F- x SR da o —sH6 oO 2 = z —47 — 45 2 a 4-— —42 = oO oO = os = = 43a wo 3-— yu wo a 4 2 -— LAB ye + 0 SYMBOL HARWELL WOOLWICH NEW YORK 1954 | t 4955 1956 | + oO x —42 2 _I, 0 1957 Fig. 6—Sr*™in Somerset milk. A comparison of the milk activity with the total fallout shows that, whereas the latter has increased fairly steadily for the pa * three years, the former rose quickly from about 2 to 5 S.U. in the spring of 1955 and has thereafter stayed fairly constant. The median of thirteen 1956 samples is 4.4 S.U., compared with 4.1 S.U. in 1955. The general trend is consistent with the theory that the milk activity is determined partly by the cumulative fallout and partly by the rate of fallout. In October and again in December 1956, samples of dried milk from various parts of Britain were obtained, and Sr®™ and Sr®° determinations made, with results shown in Table 5. There is Table 5—-REGIONAL COMPARISON OF Sr*® AND Sr®* IN DRIED MILK Date of Sr, Sr?o SrBt Ratio Area manufacture, 1956 pe/e Ca puc/g Ca ppe/g Ca Sr® /gr® Carmarthen Carmarthen Yorkshire Oct. 17 Dec. 29 Oct. 16 200 8.0 7.2 4.3 190 30 53 23 4.2 12 Yorkshire Cumberland Cumberland Antrim Dec. Oct. Dec. Oct. 3.9 6.5 5.6 6.9 19 100 5 150 4.8 15 0.8 22 Antrim 27 19 25 19 240 410 Londonderry Oct. 17 Dec. 28 270 Londonderry Somerset Somerset Dec. 27 Oct. 26 Dec. 28 280 230 7.0 24 3.4 10.3 220 21 6.2 4.6 5.5 22 110 25 3.6 24 4.5 a tendency in both sampling periods for the Sr*° activity to be higher in milk from the North and West of the British Isles than in that from the South and East. This is probably an effect of rainfall amounts. The activity of just over 10 S.U. found in the October sample from Londonderry, Northern Ireland compares with maxima of 10 S.U. or slightly more, reported from 218