72 THE RELATION OF BACTERIA TO DISEASE 



active artificial immunity because it has been given the 

 poisons themselves in such a manner that its blood 

 has been able to develop anti- or against-poisons or 

 antitoxins, strong enough to neutralize the toxins of 

 the diphtheria bacilli. This blood is suitable to be 

 transferred to another individual, and in the body of 

 the latter offsets the effects of the toxin of the diph- 

 theria bacillus. In other words, the horse's economy 

 has worked actively against the poison, whereas the 

 person receiving the horse's serum has not worked, 

 but merely received a neutralizing substance from the 

 horse's serum; it has been passive. This passive 

 immunity is also seen in the treatment of tetanus by 

 an antiserum (see Antitoxins), and lately Flexner has 

 elaborated a method by which the poisons of the 

 meningitis coccus are neutralized, here again by using 

 the serum of horses injected with this coccus. 



Artificial immunity is one that has been produced 

 intentionally by the physician. The term may be 

 correctly applied to any form except the natural or 

 active acquired immunities, but it is usually reserved 

 for the various procedures in experimental medicine 

 whereby antiserums or vaccines are manufactured. 



Anti-endotoxins. These bodies, comparable to anti- 

 toxins, are developed in the blood serum when the 

 system harbors bacteria whose pathogenic power 

 depends upon intracellular poisons. Many kinds of 

 anti-endotoxins or antibodies (a term embracing anti- 

 toxins also but more commonly used, as here) are 

 formed. The important ones are discussed under the 

 Actions of Bacterial Toxins and their Antibodies. 



