40 
BACTERIOLOGY. 
Bacterio- 
lysins 
Agglu¬ 
tinins 
Opsonins 
Comple¬ 
ment 
fixation 
tissues to form substances, circulating in the blood- 
serum, which combine with and neutralize the poisons 
of bacteria. They are spoken of as antibodies and act 
in different ways; some, called bacteriolysins, dissolve 
the bacterial cells; others gather the bacteria into 
clumps or clusters; these are called agglutinins; and 
finally substances may be formed that act on the bac¬ 
teria in such a way as to make them more readily 
digested by the phagocytes; these are called opsonins. 
It is an interesting fact, and one of much impor¬ 
tance, that the amount of these protective substances 
formed is,not only sufficient to render an infection 
harmless, but is greatly in excess of the needs of the 
moment. They remain stored away in the cells ready 
to be utilized when the same infective agent again 
attacks; this is the way that immunity is established. 
It has long been known that the blood serum of 
normal individuals contained substances that destroy 
bacteria to a variable degree. In individuals made 
immune to disease this bactericidal power of the blood 
serum is greatly increased. It developed from experi¬ 
ments made by Bordet that this destructive effect of 
the blood serum could be reproduced in animals im¬ 
munized to the red blood corpuscles of other animals. 
For example, if a rabbit be immunized gradually to 
the red blood cells of man, the rabbit’s blood serum 
will dissolve or hemolyze the human red blood cells 
when mixed with them in the proper proportions. It 
is not, however, one single substance in the rabbit’s 
serum that produces this effect but two substances, one 
