THE STREPTOCOCCUS GROUP 309 
with streptococci resulting in a severe inflammation, mastitis or 
garget, which may lead to loss of function of one or more quarters 
of the udder. It is probable from the investigations of Smith and 
Brown^ that streptococci of bovine origin are not commonly the 
etiological agents of septic sore throat in man. Studies by Jones' tend 
to confirm this contention that udder types of streptococci, which are 
usually of the mastitis type, may usually be disregarded as incitants 
of milk-borne epidemics of sore throat. Streptococci of human origin 
must be held res|)onsi})le for such epidemics in all probability. 
Immunity and Immunization.— Streptococcus infections, mild or 
severe, with the apparent exception of scarlet fever, 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 or structure, as for example, a joint, where they may 
cause a chronic, obstinate arthritis. It is possible that various strains 
of streptococci which cannot be differentiated by our somewhat arti- 
ficial cultural criteria may exist, and that subsequent infectioji may be 
with another strain. A similar condition exists in lobar pneumonia. 
Van de Velde^ has stated that the serum of an animal immunized 
against one strain of streptococcus will protect against the homologous 
strain, but not against heterologous 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 persisted 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.'* 
Rabbits have been actively immunized to streptococci through 
repeated vaccination, first with killed cultures, then with 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 consider- 
ably 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 
antitoxic content, if indeed there be any, is unknown. The chief 
demonstrable change in the serum appears to be an increased phago- 
cytic power causing leukocytes in vitro to take up more streptococci 
» Loc. cit. 2 Jour. Exp. Med., 1920, 31, 347. 
3 Centralbl. f. Bakteriol., 1898, 24, 688. 
^ 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. 
