Passive Acquired Immunity 117 



factors not originating in the animal protected, but arti- 

 ficially or experimentally supplied to it. The fundamental 

 principle is simple and has become the basis of serum thera- 

 peutics. If the immunized animal generates factors by 

 which the infecting bacteria can be destroyed or the activity 

 of their products overcome in its body, cannot these fac- 

 tors be removed and the benefit they confer transferred to 

 another animal? 



The first experiments in this direction seem to have 

 been made by Babes and Lepp,* who found that the 

 blood-serum of animals immunized to rabies showed a 

 defensive power when injected into other animals. Ogata 

 and Jasuharaf found that the subcutaneous injection of 

 blood-serum from an animal immunized against anthrax 

 enabled the injected animals successfully to resist infection. 

 Behring and KitasatoJ found that the blood-serums of 

 animals immunized against diphtheria and tetanus, when 

 mixed with cultures of these respective bacilli, neutralized 

 their power to produce disease. Kitasato found that if 

 mice were inoculated with tetanus bacilli, they could be 

 saved from the fatal infection by the infra-abdominal in- 

 jection of some blood-serum from a mouse immunized 

 against tetanus, even after symptoms of the disease had 

 appeared. Ehrlich|| showed that the blood-serums of animals 

 immunized against abrin and ricin could save other animals 

 from the fatal effects of these respective toxalbumins ; Phis- 

 alix and Bertrand,** and, later, Calmetteft found the blood- 

 serum of animals, immunized against the venoms of serpents, 

 similarly possessed the power of neutralizing the poisonous 

 effects of the venoms. KosselJJ found that the blood-serum 

 of animals, immunized against the poisonous blood-serum of 

 eels, contained a body which destroyed or neutralized the 

 effects of the eels' serum. 



Thus, it is shown that in each case in which defensive reac- 

 tions are stimulated in experiment animals, these reactions are 

 accompanied by the appearance in the blood-serum of those 



* "Annales de 1'Inst. Pasteur," 1889, vol. m. 



t "Centralbl. f. Bakt.," etc., ix, p. 25, 1890. 



| "Deutsche med. Woch.," 1890, No. 49. 



"Zeitschrift fur Hygiene," 1892, xu, p. 256. 



)| "Deutsche med. Wochenschrift," 1891, Nos. 32 and 44. 

 ** "Compte rendu Acad. des Sciences de Paris," cxvm, p. 556. 

 ft "Ann. de 1'Inst. Pasteur," 1894, vm, p. 275. 

 }J "Berliner klin. Woch.," 1898, p. 152. 



