98 Immunity 



against tetanus, even after symptoms of the disease had 

 appeared. Ehrlich* showed that the blood-serums of ani- 

 mals immunized against abrin and ricin could save other 

 animals from the fatal effects of these respective alkaloids. 

 Phisalix and Bertrand,f and later Calmette,J found the 

 blood-serum of animals immunized against the venoms of 

 serpents, similarly possessed the power of neutralizing the 

 poisonous effects of the venoms. Kossel 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 re- 

 actions are stimulated in experiment animals, these reactions 

 are accompanied by the appearance in the blood-serum of 

 those animals of factors that can be utilized to defend other 

 animals in whose bodies no similar reactions have been pro- 

 duced. 



When the defensive action departs from the simple type, 

 and is complicated by the necessary association of immune 

 and complementary bodies, the difficulty of producing passive 

 immunity increases because two factors must be simultane- 

 ously present in the serum used. Thus, to enable an animal 

 to destroy or dissolve an infecting micro-organism by which 

 it is invaded and which its own defensive mechanisms cannot 

 overcome, it is insufficient to inject the serum of an animal 

 immunized against that bacterium, because such serum 

 contains only an increased quantity of the immune or in- 

 termediate body, and no increase in the complement. The 

 animal may need no additional immune body, or, receiving 

 it, may be unable to use it because of deficient complement, 

 and under such circumstances may even be injured by it, 

 through the formation of anti-immune body by which com- 

 plementary substance subsequently formed may be rendered 

 inactive because of the neutralized immune body present in 

 its blood. It is, therefore, doubtful whether an immune 

 serum will be useful in assisting the animal i. e., producing 

 passive immunity in these cases. 



On the other hand, the administration of a serum contain- 

 ing complementary substance is made difficult because of 



* " Deutsche med. Wochenschrift," 1891, Nos. 32 and 44. 

 t " Compte rendu Acad. des Sciences de Paris," cxvin, p. 556. 

 t " Ann. de 1' I list. Pasteur," 1894, vin, p. 275. 

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



