A rupture of the integument was shown to be essential for the transmission ofGaffkya homarito the lobsterHomarus americanus. The acidity of the lobster gastric fluid was bactericidal forG.homariand was an adequate barrier against transmission of gaffkemia by the oral route. Lytic activity associated with the larger protein molecules of lobster gastric fluid, but not with the bactericidal effect of the acid condition, was weakly active againstMicrococcus lysodeikticusbut was not active againstG.homari. The acidity of the lobster stomach is a function of the acidic protein molecules rather than a result of an excess of small, acidic molecules.