CHAPTER XIV 

 ANTITOXINS 



FOR general purposes the antibodies produced during infection may 

 be divided into two groups, the first consisting of those antibodies that 

 are truly antagonistic to the bacterium or its products responsible for 

 their production, and the second those that are not in themselves de- 

 structive, but that probably prepare the bacterium for the action of a 

 more powerful antibody of the first group. 



To the first group belong the antitoxins, which neutralize the toxins 

 of a bacterium without being directly destructive to the microorganism 

 itself; and the bacteriolysins, which are truly destructive, causing the 

 bacterium to break up and finally disappear. 



To the second group belong the opsonins, which, as we have seen, 

 prepare the bacterium for phagocytosis; and the agglutinins and pre- 

 cipitins, which, while not in themselves destructive, probably in some 

 manner prepare their antigen for the action of bacteriolysins, just as 

 opsonins prepare them for phagocytosis. 



Definition. Antitoxins are antibodies in the blood that are capable of 

 directly and specifically neutralizing the dissolved toxins that caused their 

 production. 



Historic. Bacteriolysins were discovered before antitoxins. Their 

 discovery is due to the researches of Nuttall, Fodor, Buchner, and others, 

 who showed that normal serum, and especially the serum of animals 

 artificially immunized against a certain bacterium, was able to exert a 

 destructive action on the microorganism, causing its dissolution and 

 final disappearance. This property of the blood-serum was found to 

 diminish with age, and to disappear completely when the serum was 

 heated to 56 C. Buchner laid greatest stress upon the importance of 

 the thermolabile substance which he called alexin, but later researches 

 have shown that the main factors are the specific bacteriolysins, which, 

 however, are practically powerless to destroy their antigen without the 

 cooperation of alexin (later renamed " complement" by Ehrlich). 



While these studies were being made, in the hope of thus explaining 

 all phases of immunity, Behring discovered that in diphtheria infections 



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