24 INFECTION AND RESISTANCE 



numbers or in attenuated form, may produce a purely localized in- 

 fection, and ordinarily non-pathogenic germs like proteus, subtilis, 

 or colon bacilli may produce localized abscesses in weak and debili- 

 tated individuals, though implanted upon a healthy subject they 

 would be rapidly disposed of without gaining even a preliminary 

 foothold. Such tendency to localization is the common form of in- 

 fection in the case of a number of germs. It is the most usual type 

 of staphylococcus infection, for instance, in which the degree of 

 virulence of the strains ordinarily met is such that the balance struck 

 by them with the average defensive powers of man results in localiza- 

 tion. However, the same micro-organism, enhanced in virulence, or 

 gaining entrance in unusual numbers in a weakened individual, may 

 rapidly spread from the point of inoculation, at first by contiguity, 

 then by invasion of the blood and lymph channels, and become 

 generalized. 



When organisms become generalized and circulate in the blood 

 the resulting condition is spoken of as septicemia or bacteriemia. 

 This is the form of infection commonly caused by streptococci, 

 bacilli of the hemorrhagic septicemia group, anthrax bacilli, and 

 many others. It implies a powerful invasive property and always 

 constitutes a condition of great- gravity when persistent. We are 

 learning of recent years, however, that in many infectious diseases 

 formerly regarded as purely localized a temporary entrance of the 

 bacteria into the circulation is a usual occurrence. Thus Fraenkel 44 

 has shown that lobar pneumonia is almost always accompanied dur- 

 ing the acute stages of the disease by pneumococcus septicemia, and 

 in typhoid fever we now know that the organisms circulate freely in 

 the blood during the first two weeks of the disease, and often longer 

 than this. 



In these and other conditions the bacteria may be gradually de- 

 stroyed and disappear from the blood stream as the immunity of the 

 subject increases. In other cases the bacterial activities may be 

 partially checked, the process becoming slower and more chronic. 

 This is especially often the case when micro-organisms after entrance 

 to the circulation have found a secondary lodgment upon a heart 

 valve, from which a continuously renewed supply of bacteria can 

 be given off to the blood. A special form of such "malignant endo- 

 carditis" caused by the Streptococcus viridans is particularly apt to 

 take this chronic course. 



The presence of bacteria in the blood is not, therefore, as for- 

 merly supposed, an invariably fatal condition. 



Adami's recent work would indicate, moreover, that bacteria may 



normally enter the portal or even the general circulation from the 



intestine during health. This condition of "sub-infection," as he 



calls it, is more fully discussed on p. 234. That colon and other in- 



44 Fraenkel. V. Leyden Festschr., 1902. 



