Sepsis, or, more strictly speaking, bacteremia, is a phenomenon of infectious disease more and more frequently encountered as bacteriologic studies of the blood are more carefully made; positive blood cultures encountered in the routine laboratory work of large hospitals are now of very common occurrence. Most of the organisms found as microbic agents in blood stream invasion are commonly known pathogens, such as the typhoid bacillus, pneumococcus and staphylococcus; or such commensal bacteria asStreptococcus viridans, which is a normal inhabitant of the throat,1andStaphylococcus albus, which grows harmlessly on the skin surfaces—bacteria that become pathogenic only as they leave their normal fields of activity. But whereasStreptococcus viridansis one of the commonest organisms found in blood stream infections—the cause of the vast majority of cases of endocarditis lenta—another commensal inhabitant of the gastro-intestinal tract, the colon bacillus, is one of the least frequently encountered in septic