THE state of septicemia is caused by the entry of bacteria into the blood-stream, where the organisms multiply, and by reason of the multiplication exert a toxic action on the tissues of the body which is frequently fatal. In pyamia not only is there septicemia, but the circulating bacteria have also a tendency to aggregate and to lodge as emboli in end-organs and joints and there readily lead to the formation of abscesses. With pyaemia there is usually an extensive primary focus of infection. Both these pathological states have to be distinguished from bacteriamia in which condition bacteria are present in the blood-stream, and do indeed multiply there so that they may be demonstrated by blood-culture, but the blood-stream invasion is only the preliminary phase of a more defined disease process. Examples of bacteriaemia are the early stages of typhoid fever and, often, the invasive stage of lobar pneumonia.
Portals of Entry.-The disease is frequently cryptogenic, so that no portal of entry can be discovered, but there is no doubt that virulent and invasive organisms may penetrate an unhealthy mucous membrane, especially in the pharynx, without exciting a local reaction sufficiently characteristic for a clinical examination to differentiate it from any other local inflammation. Moreover, abrasions of the skin may be microscopic only, and here again the local reaction following upon penetration by organisms may be so small that even if not unnoticed it may nevertheless appear almost trivial. Usually the portal of entry is clear or may be surmised with fair confidence. In parturient women the large raw area of the placental site provides a ready entrance for bacteria. With an extensive local focus of infection, such as cellulitis or osteomyelitis, there is always a danger of blood-stream invasion, whilst septicaemia is the usual accompaniment of spreading gangrene, more especially if this arises from an infective thrombosis. In some, the injury caused by a dental extraction or by ill-timed surgical interference with a vascular but not purulent inflammatory lesion may let loose organisms into the bloodstream ; in others, the inoculation may be accidental from a minute cut or a prick, and it is obvious that the risk of septicaemia is great with war wounds, when there is great laceration of tissue and involvement of deep structures ; in others, septicaemia may be the terminal condition of an infective disease which finally invades the blood-stream after having worn down the local and general resistance of the infected subject.
Bacteria.-The bacteria most commonly responsible for the cryptogenic and puerperal forms of septicaemia are P-haemolytic streptococci of group A and, occasionally, groups B, C, D, and G ; in puerperal cases the streptococcus is sometimes an anaerobe. P-haemolytic streptococci are also the menace that lies hidden in a sometimes minute wound acquired in the post-mortem room or