THE STREPTOCOCCUS GROUP 277 



Immunity and Immunization. Streptococcus infections, mild or 

 severe, do not appear to induce any considerable degree of active 

 immunity. Not infrequently recovery is a matter of some time; the 

 acute symptoms may abate and the organisms disappear from the 

 blood stream, only to localize in some internal organ, a structure as for 

 example, a joint, where they may cause a chronic, obstinate arthritis. 

 It is possible that various strains of streptococci which can not be 

 differentiated by our somewhat artificial cultural criteria may exist, 

 and that subsequent infection may be with another strain. A similar 

 condition exists in lobar pneumonia. Van de Velde 1 has stated that 

 the serum of an animal immunized against one strain of streptococcus 

 will protect against the homologous strain, but not against hetero- 

 logous strains of streptococci, a somewhat parallel situation. On the 

 other hand, experiments are recorded which are not in accord with 

 this hypothesis. A patient suffering from an inoperable tumor was 

 inoculated subcutaneously with a culture of streptococcus; the 

 inoculation resulted in a moderately severe erysipelas which per- 

 sisted for about ten days; when the inflammation had subsided a 

 second reinoculation was made in the same place, and a secondary 

 erysipelatoid inflammation spread over the same area. A third 

 inoculation resulted similarly. These experiments indicate that this 

 patient did not develop immunity at the site of infection. 2 



Rabbits have been actively immunized to streptococci through 

 repeated vaccination, first with killed cultures, then gradually 

 increasing doses of living, virulent organisms; eventually the animals 

 will resist successfully several times the original fatal dose of the 

 homologous strain. Active immunization with polyvalent vaccines 

 containing many strains of streptococci from lesions is considerably 

 more efficient in protecting the animal against subsequent infection 

 with heterogeneous strains. The sera of such actively immunized 

 animals do not possess noteworthy antihemolytic properties; their anti- 

 toxic content, if indeed there be any, is unknown. The chief demon- 

 strable change in the serum appears to be an increased phagocytic 

 power, causing Jeukocytes in vitro to take up more streptococci than 

 they would normally. The injection of sera of actively immunized 

 animals appears to increase the resistance of non-immunized animals 

 to otherwise fatal amounts of streptococci. 



1 Cent. f. Bakt,, 1898, xxiv, 688. 



2 Coley has injected streptococci into malignant tumors with occasional beneficial 

 results; the observations are too few to warrant any definite statement of the efficiency 

 of the procedure. 



