BALANCED PATHOGENISM; EPIDEMIOLOGY 107 



BLOOD: 



Streptococcus and pneumococcus group. 



Staphylococcus group. 



Typhoid, paratyphoid and dysentery group. 



B. coli. 



Recurrent fever and treponemata. 



B. pestis. 



Certain filterable viruses: Yellow fever, poliomyelitis (?). 



Tubercle bacillus (occasionally). 

 INTESTINAL CONTENTS, FECES: 



B. bifidus and B. acidophilus group (chiefly in infants). 



B. coli, B. lactis aerogenes, proteus and cloacae group. 



Alcaligenes, paratyphoid, typhoid and dysentery group. 



Streptococcus and Micrococcus ovalis groups. 



Mucosus capsulatus group. 



Spore-forming group: Aerobic B. mesentericus, B. subtilis, B. anthracis. 



Anaerobic B. aerogenes capsulatus, B. tetani, B. botulinus. 



Acid-fast group: tubercle bacilli, bovine and human; grass bacilli. 



Spiral group: Vibrio cholerse, Sp. of Finkler and Prior. 



E. Where and How Bacteria Escape from the Body. It appears 

 from foregoing considerations that those microorganisms which are 

 progressively pathogenic for man habitually invade the tissues through 

 atria characteristic for each microbe. Their escape from the tissues 

 through appropriate channels in direct communication with the out- 

 side is equally important. Bacteria of the "opportunist" type fre- 

 quently perish within the tissues because they lack a perfected 

 mechanism of escape to the outside. Progressively pathogenic bac- 

 teria leave the body through two principal avenues the mouth and 

 nose, and the feces. Less commonly, certain types may pass to the 

 outside in the urine. The skin is not a very important factor in the 

 elimination of pathogenic bacteria. The paths of pathogenic bacteria 

 from the tissues to the outside are varied, but very constant for each 

 special organism and the discussion of this phase of their activity is 

 reserved for the Section on Specific Organisms. 



VI. BALANCED PATHOGENISM; EPIDEMIOLOGY. 



It has been helpful, for clearness and discussion, to distinguish 

 rather sharply between parasitic and pathogenic bacteria and in a 

 majority of specific instances such a differentiation can be readily 

 established. There is no hard and fast line of demarcation, however, 

 between organisms of the "opportunist" type and those progressively 

 pathogenic, for it is undoubtedly true that some "opportunists" may 

 exhibit epidemic tendencies for limited periods if a combination of 

 conditions arise which favor the distribution of the organisms and 

 either increase the invasive powers of the microbe or decrease the 

 resistance of the host. The limited spread of such bacteria is far more 



