Under laboratory conditionsBact.salmonicidamultiplies in unaltered domestic sewage and survives therein for 15 days. Removal, destruction or diminution of the original sewage flora resulted in marked multiplication ofB.salmonicidainocula, and in survival periods of from 13 to 67 days. Viability figures derived from laboratory procedures may not be directly applicable in interpreting the fate ofB.salmonicidareleased under natural conditions into natural waters.