PHENOMENA FOLLOWING IMMUNIZATION 85 



Foa, Emmerich, Bouchard, and many others. The discovery of 

 passive immunization established the fact of specific alteration of 

 the blood by active immunization, and represented, for the time, 

 a distinct triumph for the humoral hypothesis. 



Summarizing the knowledge of immunity as it stood at the close 

 of this period, Behring says : "In the case of natural immunity no 

 generally applicable explanation has as yet been found. (By this he 

 referred to the lack of complete parallelism between natural im- 

 munity and either the bactericidal or the phagocytic activities.) For 

 artificial immunization, however, it has now been shown, in a number 

 of carefully studied infections, that we can surely attribute it to 

 properties of the cell-free blood." 



Within a very short time after Behring and Kitasato's first paper 

 Ehrlich 20 demonstrated that the principle discovered by them was 

 not limited to bacterial poisons. He was investigating immuniza- 

 tion against ricin in mice, and showed that here, too, the blood of 

 the immune animals contained a body which would antagonize the 

 toxic action of ricin, and which, injected into normal mice, would 

 passively protect them. He spoke of this blood constituent as "anti- 

 ricin." 



It is natural that extensive generalization followed these discov- 

 eries. However, while it was found that the blood of all actively 

 immunized animals possessed a certain degree of protective power 

 for normal individuals, it was soon shown that this was not due in 

 all cases to antagonism to the bacterial poisons on the part of the 

 immune blood serum. In immunity to the ^ 7 lbrio Metchnikovi in 

 pneumococcus and cholera immunity Sanarelli, 21 Isaeff, 22 Pfeiffer 

 and Wassermann, 23 and a number of others showed that here, unlike 

 diphtheria and tetanus, the protective power of the immune serum 

 did not rest on "antitoxic" properties, but rather on antagonism to 

 the bacteria themselves. It soon became definitely established that 

 antitoxic immunity resulted only in the cases of those bacteria in 

 which a true soluble exotoxin was produced, and where the disease 

 following infection was primarily due to the absorption of these 

 poisons. The antibodies incited in the blood of toxin-immune ani- 

 mals were therefore spoken of by Behring and Ehrlich as "anti- 

 toxins" and their action after a number of false hypotheses was 

 finally recognized as a direct neutralization of the bacterial poisons. 



The strict specificity of these antibodies was, from the first, clear 

 to v. Behring, who observed that diphtheria-immune serum and 

 tetanus-immune serum acted each upon its respective toxin only. It 

 was recognized at the same time that the passive immunity produced 



20 Ehrlich. Deutsche med. Woch., No. 32, 1891. 



21 Sanarelli. Ann. Past., Vol. 7, 1893. 



22 Isaeff. Ibid, and Zeitschr. f. Hyg., Vol. 16, 1894. 



23 Pfeiffer and Wassermann. Zeitschr. f. Hyg., Vol. 14, 1893. 



