IMMUNITY 73 



Antitoxins. The production of antitoxins hinges on 

 this subject. Antitoxins may be described as the 

 substances produced in the blood or blood serum 

 of animals injected with the poisons elaborated by 

 bacteria, but soluble and separable from the germ cells. 

 The toxins used to make the injections into animals 

 are obtained by growing the bacteria in broth and 

 then filtering off their bodies. They are distinguished 

 from the poisons described in a preceding paragraph 

 in that no destruction of the germs is necessary to 

 produce these separable toxins. 



Recapitulation. To recapitulate briefly, active ac- 

 quired immunity is produced by injection of living 

 bacterial cells when incapable of producing disease, 

 or by their endocellular poisons or extracellular 

 separable toxins. In the case of the latter it is possible 

 to take from the blood serum of the immune animals 

 something which will neutralize the toxins introduced, 

 in other words, the principle involved in making of 

 diphtheria and tetanus antitoxin. The former, non- 

 virulent germs or their poisons, is used now as the 

 basis of bacterin treatment. 



Action of Bacterial Poisons and their Antibodies. This 

 matter is very complicated and not by any means 

 perfectly understood by the most profound scientists. 

 It is, moreover, unnecessary to enlarge upon it in a 

 work of this kind, and tracing the methods as simply 

 as possible is sufficient. 



The free soluble toxins stimulate the production 

 of antitoxins which have an attraction for the toxin, 

 and for it only. Therefore, when any free toxin and 

 free antitoxin come together they combine, and one 

 neutralizes the other. 



