GENERAL BACTERIOLOGY 
63 
exotoxin, nevertheless, there has already accumulated 
enough poison to kill the body; for this reason a sub¬ 
stance is produced that does not attack the bacteria 
but neutralizes the exotoxin; this substance is called 
‘ ‘ antitoxin. 5 ’ 
It is very important to know that the early opinion 
that the antitoxin actually destroys the exotoxin is er¬ 
roneous; it prevents the action of exotoxin not by de¬ 
stroying it, but by neutralizing it, the mixture of exo¬ 
toxin and antitoxin being neutral much in the same 
manner as the mixture of an acid or alkali is. 
When bacteria act by producing not the exotoxin hut 
the endotoxin, it is apparent that it would be useless 
for the body to produce antitoxins, and the body in 
such cases produces several antibodies (not one, as in 
the case of exotoxins). 
1. Bacteriolysins (bacteria, and Greek lysis, mean¬ 
ing solution); these are the substances which cause 
the bacteria to swell up, become granular, and finally 
undergo a complete solution. 
2. Agglutinins (from Latin, meaning glue); these are 
substances which cause the bacteria to lose their motil¬ 
ity if they are motile, and then clump in small or large 
groups. 
Agglutinins are not really immune bodies, because 
clumped bacteria are just as dangerous and virulent as 
those that are not agglutinated, and are mentioned here 
because of their importance in diagnosis of certain in¬ 
fectious diseases. 
3. Precipitins are substances which cause bacterial 
culture filtrates when mixed with the blood serum to 
form precipitates. Like agglutinins they are not true 
immune bodies, but are formed by bacterial invasion, 
and for this reason are mentioned here. 
4. Opsonins (from Greek opsonein, meaning prepare 
