“…Thus in tests in guinea-pigs the B.C.G. substrain used in the Puerto Rico trial was reported as showing less immunizing potency than several others, including the Phipps substrain used by Aronson et al; one substrain from the laboratory supplying the Georgia/Alabama trial showed low, and another from the same laboratory high potency (Willis et al, 1960;Willis and Vandiviere, 1961). Though these tests were made some years after the trials, and therefore cannot be conclusive, I shall give later some additional indirect information on this point.…”