304 STUDIES IX I.UMIMTY. 



that the collaboration of two substances was necessary for the 



bacteriolysis of the cholera vibrio. We were able to satisfy our- 

 selves that an animal immunized with cholera serum, and thereby 

 acquiring, as Fraenkel and Sobcrnhehn showed, a bacteriolytic 

 power in their body fluids, owes this newly obtained power to, 

 first, the alexin already present in the normal animal, and, secondly, 

 the specific sensitizer in the injected cholera- serum. The bac- 

 tericidal power, then, is generated in the fluids of the treated animal 

 as it is in a test tube containing fresh normal serum on the addition 

 of a little anticholera sensitizer. In either instance a combination 

 of the two substances is required.* The fact that the immunity 

 soon disappears is due simply to disappearance of the sensitizer 

 from the fluids. 



This explanation of the transitory nature of passive immunity 

 is doubtless correct in those instances in which the injected serum 

 comes from animals of the same species. But it has been noted 

 by several observers that the duration of the immunity is remark- 

 ably short when the serum is obtained from an alien species. f 

 Pfeiffer and Fried berger offered the plausible hypothesis in the 

 case of cholera serum that, when passive immunity disappears very 

 rapidly, it is owing to the fact that the treated animal reacts to the 

 substances injected by elaborating antagonistic substances, like 

 antisensitizers, that neutralize them. 



The question may well arise as to whether animals of species A 

 inoculated with any immune serum from species B (antitoxins, 

 agglutinins, lactoserum and so forth) do not form antisubstances 

 to them, comparable to those that neutralize hemolytic sensitizers. 

 As we have noted, Pfeiffer and Fried berger obtained an anticholera 

 serum and Schiitze$ has obtained an antilactoserum. Kraus and 

 Eisenberg§ have made systematic studies of these substances and 

 failed to find in the serum of treated rabbits substances capable 

 of neutralizing the diphtheria antitoxin or the typhoid agglutinins 

 present in specific sera from the horse. Such results appear irrecon- 



* See p. 80. 



t See particularly among recent articles, Schutze, Ueber das Verschwinden 

 verschiedener Immunsera aus dem tierischen Organismus. Festsch. v 60 Geburt- 

 stag. v. R. Koch, p. 657. 



t Schutze, Berlin, klin. Wochen., 1901, No. 50, 1263. 



§ Kraus and Eisenberg, Cent. f. Bakt. Orig. XXXI, 1902, 208. 



