320 INFECTION AND IMMUNITY 



ganisms have been introduced directly into the circulation in quantities 

 sufficient to bring about a very rapid poisoning and overwhelming of the 

 animal, with probably only a very partial adaptation of the bacteria 

 to the animal agents of resistance. On the other hand, the septicemic 

 invasion in man most often follows the adaptation of the germs in some 

 more favorable nidus, and probably has to do with an evolution in the 

 bacterial resistance to the protective powers, rather than a decrease in 

 protective strength on the part of man. Indeed, both of these processes 

 may increase hand in hand, and we may have septicemias extending over 

 weeks, months, and even years. We may have, in fact, an " armed 

 peace" and the prepared bacterial army is not to be routed by the 

 application of means which under other circumstances might prove effi- 

 cacious, for we have seen how the bacteria may possibly become resist- 

 ant to the protective agents of the animal body, and may continue to 

 survive attacks which might well prove fatal to less well-adapted 

 members of their species. An excellent example of this is our own 

 recent experience with the treponema pallidum which in its virulent 

 condition resists serum influences which strongly agglutinate the culti- 

 vated non-virulent strains. 



