25.63 + 029 ——~ 29.57 + 0.26 ——-~ 20.44 + 066 ——. 34.72 + 0.346 —— 24.24 + 0.45 ———- ul pyc Sr9YG Ca 0 | | MsJASONDIJFMAMJ J ASONODISFMAMIJIJVASOND|Y FMAM J 1955 1956 1957 1958 Fig. 11— Monthly Sr®® levels in Mandan, N. Dak., powdered milk, 1955 1956 1957 Fig. 12— Monthly Sr®° levels in Columbus, Wisc., powdered milk. a9