SUMMARY: In stock cultures of strain 2 carrying the factor determining the production of colicine I, , together with other colicine factors, or , most of the small minority of bacteria competent to act as donors of also transmit their E factor. Most noncolicinogenic bacteria which acquire an E factor at the same time as become competent to transmit both factors. Similarly, bacteria carrying factors and/or accept normally and then usually become competent to transmit both and the E factor(s) they already carry. In experiments on the kinetics of colicine factor transmission by 2 () () newly infected with , most acceptor bacteria that acquire any colicine factor acquire all three factors, within 5–20 min. for most pairs, but within 1 min. for a very few. When conjugation is interrupted within 5 min. of mixing, fewer acceptor bacteria acquire all three factors; all single-factor and two-factor classes are then represented, so the order of transfer of the three factors must differ in different pairs. Bacteria carrying do not transfer this factor to donor bacteria from whom they acquire ; but they become able to transmit (and presumably also) within 15–20 min. of acquiring Other observations support the hypothesis that in most competent donors carrying and/or , these factors multiply autonomously, as does


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