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Ability to produce colicines I, El, E2, K or B was transferred to Salmonella typhimurium strain LT2 by growth in broth with suitable colicinogenic strains of Escherichia coli or ShigeZZa sonnei. When LT2 (coll), i.e. carrying the colicine I factor, or LT2 (coZB) were grown overnight in broth with LT2 coZ-(non-colicinogenic), c. 50 yo of the latter became colicinogenic; LT2 (coZE2) and LT2 (coZK) did not transmit; LT2 (colEI) transmitted to only c. 0.1 yo of the acceptor population. But LT2 carrying either COZI or colB in addition to coZE2, coZK or coZE.2, transmitted both factors.When overnight broth cultures of LT2 (coZI) and LT2 col-were mixed and incubated c . 40 yo of the latter acquired COZI by 20 hr. (when the viable count had doubled) ; but only c . 0.02 yo acquired colI in 3 hr. The low initial transfer results from the fact that in a stock culture of LT2 (coZI) only c. 1/5000 bacteria are 'competent donors', able to transmit COZI. The later large increase in the proportion of colicinogenic bacteria probably results from 'epidemic spread' of the colI factor amongst the acceptor population, initiated by the few acceptor bacteria which originally receive it. It is supposed that most bacteria which have just acquired COZI become competent donors. In a doubly colicinogenic strain most competent donors transmit both colicine factors. Aeration by shaking during incubation interfered with transmission of colicinogeny, probably by abolishing the prolonged phase of slow growth of unaerated cultures. Growth in the presence of acriflavine did not 'cure' LT2 (coZI) or LT2 (colI) (colE2) of colicinogeny, nor of ability to transmit. LT2 (coZE.2) and LT2 (coZEZj supported the epidemic spread of colI or coZB about as well as did LT2 COZ-; but in LT2 (coZK) the spread of COZI was greatly reduced and that of colB somewhat reduced. The prior presence in an acceptor strain of one of the readily transmissible factors, COZI or colB, did not interfere with the epidemic spread of the other. But LT2 (colI) did not become a competent donor on accepting coZE2 and, by inference, coZI from LT2 (coZ1) (coZE2).

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