BACTERIOLOGY: C. G. BULL 
545 
A MECHANISM OF PROTECTION AGAINST BACTERIAL 
INFECTION 
By Carroll G. Bull 
ROCKEFELLER INSTITUTE FOR MEDICAL RESEARCH. NEW YORK 
Presented to the Academy. September 21. 1915 
The means employed by the animal body to rid itself of bacteria have 
been conceived to be of two kinds: those of disintegration or lysis, and 
those of cellular inclusion or phagocytosis. 
According to the former, the bacteria are acted upon by certain con- 
stituents of the blood serum — amboceptor and complement — ^which dis- 
solve them; and according to the latter they are englobed by white 
blood corpuscles which digest them. 
As a matter of fact, the first process has been inferred, rather than 
demonstrated. It is true that in shed blood the dissolution by lysis 
has been observed, but not in the living body. But even in shed blood 
or its serum constituents the solution occurs only with a part of the 
pathogenic bacteria, of which B. typhosus may be taken as an example. 
Such bacteria as pneumococcus, streptococcus, etc., are not subject 
directly to this form of dissolution. Phagocytosis, on the other hand, 
is a more general phenomenon and applies to a wide variety of bacteria. 
It has long been known that when bacteria are introduced into and 
later disappear from the blood, they are not eliminated by the organs 
of excretion, but are destroyed in the organs themselves. The problem 
at issue relates to the manner of the destruction. 
The question should be considered with reference to two states of the 
animal body, namely, the unprotected or normal, and the protected or 
immune state. 
Taking certain forms of pathogenic or disease producing bacteria, 
a study was made as to the manner of their disappearance in protected 
rabbits. The pneumococcus and typhoid bacillus may serve as exam- 
ples. Protection was secured by the employment of immune sera. In 
the case of the pneumococci, the type of pneumococcus and immune 
serum must coincide. In the experiments a type I pneumococcus and 
corresponding serum were employed. 
Protection against pneumococcus. It has been shown that an active 
pneumococcus serum protects against a certain maximum quantity of 
pneumococcus culture, but that multiples of the serum do not protect 
equally against multiples of the culture. An effective culture of pneu- 
mococcus causes on inoculation fatal septicemia in the rabbit, followed 
