382 INFECTION AND RESISTANCE 



Lewis further showed that normal guinea pigs could be rendered 

 hypersusceptible with the blood of congenitally sensitive animals. 



Passive sensitization is carried by the blood serum purely, since, 

 in ordinary cases, as Rosenau and Anderson have shown, the blood 

 corpuscles and tissues of a sensitive animal do not convey the hyper- 

 susceptibility. An exception to this will be noted later when we 

 come to discuss Bail's experiments on the passive transfer of tuber- 

 culin sensitiveness. 



Passive sensitization, once established, may persist for as long 

 as 3 or 4 weeks, though Rosenau and Anderson found that animals 

 tested 26 days after treatment reacted but weakly. In the young 

 of anaphylactic mothers Otto has observed positive reactions as long 

 as 44 days after birth, though fatal results were obtained in pigs only 

 a few days old. 



To summarize the matter briefly, we may state that passive sen- 

 sitization may be accomplished with any serum that contains anti^ 

 bodies, and that the qualitative power of such a serum to convey 

 passive sensitization is in direct proportion to its antibody concen- 

 tration; in short the process of sensitization consists in the introduc- 

 tion of antibodies. This fact, which is, of course, of the greatest 

 theoretical importance, will be further discussed in the succeeding 

 chapter. 



Throughout the earlier investigations upon passive sensitization 

 the curious fact recurs in the experiments of successive workers that 

 a definite period must elapse between the injection of the sensitive 

 blood and that of the antigen. 



Both Friedemann and Otto found that when the sensitive serum 

 was injected subcutaneously the best results were obtained by ad- 

 ministration of the antigen 24 to 48 hours after this. On intra- 

 peritoneal injection of the sensitizing serum Doerr and Russ 80 ob- 

 tained the best results by permitting an interval of 24 hours to 

 elapse, and the same investigators still further shortened this period 

 to 4 hours by injecting the sensitive serum intravenously. Beyond 

 this, the interval could not be shortened with success. Indeed, some 

 writers, notably Gay and Southard, have claimed that the maximum 

 hypersusceptibility in guinea pigs treated with sensitive serum is 

 reached only after 10 or more days, and Rosenau and Anderson, 

 Lewis, and others have obtained results which seemed to point in 

 the same direction. However, as we have already indicated, the 

 testing of animals so long after the injection of sensitive serum 

 leaves us in doubt whether we are dealing with true "passive" trans- 

 foreign injected protein than normal ones, and this more rapidly, may never- 

 theless be not a whit more tolerant of the antigen sometimes even extremely 

 sensitive and vulnerable. 



80 Doerr and Russ. Zeitschr. f. Immunitatsforscliung, Vol. 3, p. 181,. 

 1909. 



