324 
THE STREPTOCOCCUS-PNEUMOCOCCUS GROUP 
Much light has been shed upon the apparent variability of strains 
of pneumococci by the observations of Neufeld and Handel/ and 
Dochez- and Dochez and Gillespie.^ These observers have shown 
by serological reactions that pneumococci may be divided into four 
groups or types, each of which fails to agglutinate with sera other 
than the homologous serum. These groups have been tentatively 
designated I to IV inclusive. The "type specificity" of the first three 
groups has been shown to reside in polysaccharides which have been 
studied by x\very and others.^ Groups I and II are typical virulent 
pneumococci.^ Group IIP comprises the organism formerly known 
as Streptococcus mucosus, now called Pneumococcus mucosus; and 
Group 1\ includes relatively avirulent strains which are commonly 
found in the mouths of healthy persons. Group 1\ is somewhat more 
heterogeneous, judging from agglutination reactions, than Groups I 
and III. Group III contains the most virulent organisms. A study 
of the distribution of the various types in 448 cases of pneumonia 
illustrates this point :^ 
Number 
of cases 
examined. 
Blood cultures. 
Mortality. 
Type of 
pneumonia. 
Positive. 
Negative. 
Positive 
blood culture. 
Negative 
blood culture. 
Cases. 
Per cent. 
Cases. 
Per cent. 
Cases. 
Per cent. 
Cases. Per cent 
II . . 
III . . 
IV . . 
145 
148 
' 55 
i 100 
50 
; 49 
16 
1 21 
35 
33 
29 
21 
95 
99 
39 
79 
66 
67 
79 
71 
13 
36 
16 
11 
26 
73 
100 
52 
3 3 
9 9 
11 1 28 
3 ! 4 
It is possible that "mixed infections" will be found when more 
cases are carefully studied. The same general types were reported in 
Europe and in Philadelphia.^ 
Immunity and Immunization.— Relatively little is known of the 
nature and extent of immunity following recovery from an attack of 
pneumonia. One attack appears to predispose somewhat to a sub- 
sequent attack which was explained formerly on the basis that little 
or no immunity was conferred on the patient. The extensive work 
1 Ztschr. f. Immunitatforschr., orig., 1909, 3, 159; Berl. klin. Wchnschr., 1912, 49, 680. 
2 Jour. Exp. Med., 1912, 16, 680. 
' Jour. Am. Med. Assn., 1913, 61, 727. 
* See p. 60; also Heidelberger: Chem. Rev., 1927, 3, No. 4. 
5 Group II has been shown to consist of a typical and an atypical member.' 
6 Type III, Pneumococcus mucosus, differs from Streptococcus mucosus in several 
particulars; it is bile-soluble, it is very virulent for white mice, it produces a very volum- 
inous capsule, it ferments inulin and exhibits a greenish halo around its colonies on blood 
agar. 
' Avery, Dochez, Cole and Chickering: Monograph 7, Rockefeller Institute, October 
16, 1917.' 
* Cole: New York Med. Jour., January 2 and 9, 1915, 
