68 THE RELATION OF BACTERIA TO DISEASE 



bacteria when used themselves for active immunization, 

 the germ-cell disintegrates before the poison escapes. 



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. 



In the case of the reaction of bacterial cells or their 

 endotoxins the result is more complicated. Many 

 substances are formed, again called anti-, or in general, 

 antibodies. Three will be considered: (1) The anti- 

 bodies which dissolve bacterial cells; (2) those which 

 clump them; and (3) those which encourage the white 

 cells of the blood to eat them. The substances exist 

 in minute quantities in normal blood. 



