132 
PRINCIPLES OF BACTERIOLOGY 
ism which is most likely to be confused with pneumococ¬ 
cus is streptococcus, the following points should be 
borne in mind. 
Pneumococcus 
Streptococcus 
Almost never capsulated. 
Insoluble in bile. 
Does not ferment inulin. 
Almost always capsulated. 
Soluble in bile. 
Ferments inulin. 
No hemolysis on blood plates. Hemolysis present. 
Finally, agglutination test will not only enable one to 
make a definite diagnosis, but, in cases of pneumococ¬ 
cus, will identify the type of pneumococcus. 
IX. The Different Types or Strains of Pneumococci 
As has been mentioned above there are at least four 
types of pneumococcus: 
Type I causes pneumonia in 33 per cent of cases. 
Type II causes pneumonia in 31 per cent of cases. 
Type III causes pneumonia in 12 per cent of cases. 
Type IV causes pneumonia in 12 per cent of cases. 
Mortality caused by the different types also differs: 
Type I is fatal in 25 per cent of cases. 
Type II is fatal in 32 per cent of cases. 
Type III is fatal in 45 to 50 per cent of cases. 
Type IV is fatal in 16 per cent of cases. 
The agglutination test consists in mixing the isolated 
organisms with the serum of an animal injected with 
the different types, and observing where agglutination of 
bacteria takes place. For complete technic the reader 
should consult the monograph on Acute Lobar Pneu¬ 
monia by Cole and his coworkers (The Monograph No. 
7 of the Rockefeller Institute for Medical Research). 
