546 
BACTERIOLOGY: C G. BULL 
by death in 24 to 48 hours or less. When an immune serum is employed, 
life may be saved or the surviving period merely prolonged. 
The immediate effect of a serum injection is to cause the removal of 
the pneumococci from the circulating blood. This effect is produced 
in an incredibly short period of time — in a few minutes indeed. But 
the permanency of the removal depends in part on the quantity (or 
dose) of antiserum injected. Small doses of serum are more effective 
than large doses, and the former may be successful in saving life, while 
the latter are not. 
The mechanism of the removal is as follows : when an immune serum 
is introduced into the blood of a rabbit suffering from pneumococcus 
septicemia, an almost immediate agglutination of the bacteria takes 
place. The larger the doses of the serum, within limits, the larger 
the size of the bacterial clumps that are found. The clumps are removed 
from the blood almost immediately by the organs — the spleen, liver, 
and bone marrow. What happens next is determined by the size of 
the clumps. If they are large, they cannot be ingested by phagocytes; 
hence they soon begin to multiply, and the bacteria reinvade the blood; 
if small, they are taken up by phagocytes and are digested. The ani- 
mal succumbs on the one and survives on the other hand. Hence small 
doses of the serum causing smaller clumps may be more effective than 
large doses giving larger ones. No extra-phagocytic dissolution of the 
pneumococci seems to occur. 
Protection against the typhoid bacillus. A similar mechanism operates 
in the rabbit inoculated with cultures of the typhoid bacillus. The 
typhoid bacilK, notwithstanding the fact that they are subject to serum- 
lysis, are taken out of the blood by the organs after clumping, and the 
clumps ar ingested by phagocytes which digest them. 
Pathogenic and non-pathogenic bacteria. Certain cultures of disease- 
producing bacteria are not, others are pathogenic for animals. The 
influenza bacillus appears in these two distinct varieties. When cul- 
tures by the non-pathogenic variety are injected into the circulation of 
rabbitbi, they are clumped and removed by the organs at once; when cul- 
tures of the pathogenic variety are inoculated, they are neither clumped 
nor removed. Hence a pathogenic effect may depend upon agglu tin- 
ability of the bacteria — by the blood of normal or of immunized animals. 
In other words, bacteria circulating in the blood are quickly removed 
when they are agglutinated or clumped, and the clumps deposited within 
the organs are taken up by phagocytes and digested. They appear 
not to be destroyed by solution or lysis through the operation of serum 
constitutents of the blood. 
