BALANCED PATHOGENISM: EPIDEMIOLOGY 107 
Serous Fluids: 
1. Cerebrospinal fluid: 
(a) Fluid usually clear: tubercle bacillus and Treponema pallidum. Virus 
of poliomyelitis. 
(6) Fluid turbid: pneumococcus, streptococcus, meningococcus, B. influ- 
enzae, B. typhosus, B. coli. 
2. Pleural and pericardial fluids: 
(a) Fluid usually clear: tubercle bacillus. 
(b) Fluid turbid as a rule: pneumococcus, streptococcus, B. iufluenziE, 
pneumobacillus group, B. typhosus, staphylococcus. 
3. Peritoneal fluid : 
Streptococcus group. 
Coli and typhoid group. 
Tubercle bacillus(?). 
Blood: 
Streptococcus and pneumococcus group. 
Staphylococcus group. 
Typhoid, paratyphoid and dysentery group. 
B. coli. 
Recurrent fever and treponemata. 
B. pestis. 
Yellow fever, dengue. 
Certain filterable viruses: 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: bacillus of Morgan. 
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. botu- 
linus. 
Acid-fast group: tubercle bacilli, bovine and human; grass bacilli. 
Spiral group: Vibrio cholerse, Spirilla 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 in\ade 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 which 
may accidentally enter the tissues at any point where the continuity 
of epithelia is destroyed, frequently perish within the tissues because 
they lack a perfected mechanism of escape to the outside. Progres- 
sively pathogenic bacteria 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 
