THE STAPHYLOCOCCUS GROUP 293 
.lwiwa/,s'.— Rabbits air tlie best of the lal)()rat()ry animals for 
experimental inoculation. Subcutaneous inoculations of virulent 
strains frequently result in abscess formation and the (knelopment of 
a febrile reaction. These abscesses commonly ulcerate, discharge and 
heal spontaneously. By no means do all virulent strains induce 
lesions, however,; there is great difference between them in this respect. 
Intraperitoneal injections frequently cause a rapidly fatal peritonitis 
with or without septicemia. The intravenous injection of 0.25 to 
1 cc. of an eighteen^hour broth culture usually causes a generalized 
pyemia with septic foci, particularly frequent in the kidneys and 
liver. Orth^ and Wyssokowitsch- have shown that mechanical injury 
to the heart valves prior to the intravenous injection of staphylococci 
usually causes a localization of the organisms there, producing an 
endocarditis. If a bone is injured prior to an intravenous injection, 
a typical osteomyelitis frequently results. It should be remembered 
that the pus produced by staphylococci in rabbits is more dry than 
that produced in man. Guinea-pigs are less susceptible than rabbits 
to infection with the staphylococcus. 
Immunity and Immunization.— Staphylococci do not ordinarily ex- 
hibit invasive powers for man or animals; they are usually parasitic. 
Whenever the continuity of the skin is destroyed, as by abrasion, or 
weakened, as in diabetes, the organisms reach the underlying tissues 
and induce inflammatory reactions. Repeated injections first of 
killed then of live staphylococci will frequently raise the threshold of 
infection in experimental animals to a very considerable degree, but 
the process of immunization cannot be always relied upon— many 
animals died rather abruptly with rather extensive amyloid degen- 
eration, particularly of the kidneys. Leukocytes, particularly the 
polymorphonuclear leukocytes, appear to play a prominent part in 
the immunity against staphylococci; it can be shown by experiment 
that the leukoc\''tes are more active phagocytically in immunized than 
in non-immunized animals. 
Similarly, the resistance to staphylococcus infection, which appears 
to be rather marked in the average normal man seems to depend 
largely on the phagocytic activity of leukocytes in the last analysis; 
and the efficiency of vaccines, particularly the autogenous vaccines, 
in the treatment of furunculosis has focused attention sharply upon 
the part played by opsonins in these infections. Generally speaking, 
injections of killed cultures of staphylococci in graduated doses begin- 
ning with 100 millions and increasing to 1000 millions or more at 
appropriate intervals exert a favorable influence on the course of the 
infection. The efficiency of this vaccination (active immunization) 
is attributed to the gradual development of specific opsonins (bacterio- 
tropins) which reinforce the action of normal opsonins, whose activity 
is somewhat below normal. In practice this is accomplished in the 
1 Centralbl. f. d. med. Wissensch., 1905, No. 3.3. 
2 Virchow's Arch.. 1886, 103, 301, 310. 
