ANTAGONISM B1-T\\ I-l-X THE LIVING BODY AND BACTERIA 161 



An animal already profoundly poisoned by the toxin is unaft'ected by 

 any amount of antitoxin. 



Duration of Immunity. The antitoxins of diphtheria and tetanus 

 are gradually 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 secretions, and it is 

 partly destroyed in the body. An animal which has been highly im- 

 munized will retain considerable amounts of antitoxin for from two to 

 four months. 



Stability of Antitoxins. The different antitoxins vary as to their 

 stability thus: that of diphtheria is somewhat more stable than that 

 of tetanus. Kept aseptically in cold and dark storage, and protected 

 from access of air, the more resistant antitoxins may be preserved 

 sometimes for a year or two with very little deterioration in strength. 

 At other times, however, from unknown causes, they are gradually de- 

 stroyed, so that there may be a loss of about 10 per cent, per month. 

 A serum requires, therefore, to be tested every few months if we wish 

 to be assured of its strength in antitoxin. Preservatives, such as car- 

 bolic acid, trikresol, etc., alter antitoxins only very slightly when in 

 dilute solution, but in strong solution they partially destroy them. Heat 

 up to 62 C. does not injure them greatly, but higher temperatures 

 alter them. 



Method of Administration. Antitoxins and bactericidal substances 

 are absorbed to a very slight extent only when taken by the mouth 

 certainly less than 1 per cent. They must, therefore, be introduced 

 subcutaneously or intravenously to enter the body. The antitoxic 

 serum does not act against the bacteria directly, but, by neutralizing 

 their poisons, it prevents them from acting as irritants to the cells, 

 and so the soil for the growth of the bacteria becomes unsuitable, 

 and they cease to develop. 



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