CHAPTER XIV. 



ANTITOXINS. 



THOSE substances which destroy bacteria are said to be 

 germicidal ; but those substances which neutralize the bacte- 

 rial toxin are of vastly more importance. They are called 

 antitoxins. An antitoxin is a substance which has remained 

 in the tissues and juices of the body, and which confers 

 immunity by antagonizing or neutralizing the product of the 

 bacteria. The most exhaustive experiments and researches 

 have failed to reveal the exact nature of these products, 

 although their presence in the body has been proved by many. 



It is not accepted, however, that immunity is due to the 

 presence in the body of an antitoxin. This substance is 

 looked upon as the result of forced immunization. 



Various theories as to the probable nature of this substance 

 have been advanced. All experimental evidence goes to 

 show that in certain conditions acquired immunity depends 

 upon the formation of an antagonistic substance. Antitoxins 

 usually possess no germicidal power. 



Buchner does not regard the antitoxin as a reactive prod- 

 uct, but as a modified, changed, " poison-free " product of 

 the specific bacterial cells. 



Ehrlich's side-chain theory is another theory accounting for 

 the production of the antitoxin, that it is the product of 

 excessive tissue stimulation. 



For a long time it was supposed that the antitoxin was the 

 modified toxin, but conclusive evidence against this theory is 

 now at hand : (1) The quantity of antitoxin is not at all in 

 proportion to the amount of toxin required to produce the 

 immunity. (2) The removal of large quantities of blood from 

 the body does not lessen the degree of immunity. (3) If the 

 immune animal is bled to death and the entire vascular system 

 carefully washed out with sterile salt solution until every 



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