The Chat strains 1, 2, 3 from Lederle’s were used at Wistar. Finally, possibly to air out the situation, in 1960 Cox told McBurney, the US Surgeon-General that he found Sabin 1, 2, 3 least pathogenic in new monkey trials, making Sabin the easy winner and wiping out Kaprowski. Intracerebral live virus in monkeys is a delicate trial indeed.