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. \Ve 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 



