IMMUNITY. 113 
Some other important parasitic bacteria produce 
toxins and in the body antitoxins, but all to a far less 
extent than those of tetanus and diphtheria. Follow- 
ing them is the plague bacillus, and then, but far 
behind, the cholera spirilla, the typhoid bacilli, the 
streptococci, etc. These latter bacteria produce more 
of the substances which inhibit bacterial growth than 
of those which neutralize their toxins. 
The effect of the antitoxin is to prevent the poison- 
ous action of the toxin. It does not, so far as we 
know, influence the cells after they have been injured 
by the toxin; it is, therefore, a preventive rather than 
a cure. We find, experimentally, that a very much 
smaller amount of antitoxin will neutralize a fatal dose 
of toxin in an animal, if given before or at the same. 
time, than if given only shortly after it. An animal 
already profoundly poisoned by the toxin is unaffected 
by any amount of antitoxin. 
The antitoxins of diphtheria and tetanus are gradu- 
ally eliminated from the body after their injection or 
after their production from toxin injections. After 
the usual immunizing dose the duration of immunity 
is only from two to six weeks, the period differing in 
each individual. The elimination of the antitoxin 
takes place partly through the urine and other secre- 
tions, and it is partly destroyed in the body. An 
animal which has been highly immunized will retain 
considerable amounts of antitoxin for from two to four 
months. | 
The antitoxins as contained in the serum are fairly 
stable. The different antitoxins vary thus, that of 
diphtheria is somewhat more stable than that of tetanus. 
Kept aseptically in cold and dark storage, and pro- 
8 
