ANAPHYLAXIS 381 



of ways. They themselves regarded the hypersusceptibility which 

 the injected animals developed as a "purely active one/' and it is 

 more than likely that this was the case, the recipient animals being 

 actively sensitized by traces of antigen remaining unassimilated in 

 the blood of the actively sensitized donors. In the following year 

 (1908) the facts of passive sensitization were rapidly confirmed and 

 extended by Besredka, 74 Lewis, 75 and others, 76 and information of 

 the greatest value for the comprehension of the anaphylactic reaction 

 was obtained. 



Otto showed that passive sensitization could be carried out with 

 the serum of an actively sensitized animal 8 days after the antigen 

 injection, at a period when this animal itself had not yet become 

 hypersusceptible. He also showed that the passive transfer of ana- 

 phylaxis need not be confined to animals of the same species, but that 

 guinea pigs could be rendered passively anaphylactic with the blood 

 serum of sensitized rabbits. From the work of Gay and Southard, 77 

 moreover, it appeared that not only by the blood of sensitive animals 

 can anaphylaxis be transferred, but that this can also be done by 

 injecting the blood of animals that have once been sensitive but have 

 subsequently been rendered antianaphylactic or refractory. Analo- 

 gous to this observation is the fact observed by these authors as well 

 as by Friedemann that the young of antianaphylactic mothers are not 

 refractory but hypersusceptible. This observation, unquestionably 

 correct, since it has been confirmed by several other workers, is 

 astonishing and contrary to expectation. It has had no inconsider- 

 able bearing upon our theoretical understanding of anaphylaxis. 



It was soon found out, too, that hypersusceptibility was conveyed 

 not only by the sera of sensitive and of refractory animals, but that 

 it could likewise be transferred by the precipitating sera of animals 

 systematically immunized with a foreign proteid. 



This method was later employed by Doerr and Russ 78 in their 

 quantitative studies on the relations between anaphylactic antigen 

 and antibody. We are confronted, then, with the curious facts that 

 animals may be passively sensitized : 



(a) by the serum of a sensitized animal. 



(b) by the serum of an animal not yet sensitive in the pre- 

 anaphy lactic period (8th day, Otto). 



(c) by the serum of an antianaphylactic animal. 



(d) by the precipitating serum of an "immunized' 7 79 animal. 



74 Besredka. Ann. de I'Inst. Past., Vol. 22, 1908. 



75 Lewis. Jour. Exp. Med., Vol. 10, 1908. 



76 Kraus and Doerr. Wien. klin. Woch., No. 28, 1908. 



77 Gay and Southard. Jour. Med. Res., Vol. 18, 1908. 



78 Doerr and Russ. Zeitschr. f. Immunitatsforschung, Vol. 3, 1909. 



79 We must never forget that the term "immunized" as applied to animals 

 treated with harmless protein is an analogy and not absolutely correct. 

 Such animals, though probably capable of assimilating larger quantities of 



