﻿STUDIES IN PLAGUE IMMUNITY. 237 



aggressin from that produced by the artificial product, and my sub- 

 sequent experiments, as did my earlier ones, have only further confirmed 

 the views of Wassermann and Citron 5n that the aggressins must be 

 considered to be hypothetical substances and that, so far as their immu- 

 nizing value is concerned, in these exudates we have to do mainly with 

 the sustances extracted from the bacilli themselves. Evidently, in the 

 case of the plague bacillus, the i-eceptors of the organism in the so-called 

 aggressin exudates of animals become liberated in a more efficient 

 manner for immunization and probably exist in a less altered condition 

 than they clo in the aqueous suspension of the bacilli obtained by 

 artificial means. Obviously, in natural plague aggressin no other immu- 

 nizing substances are existent than those present in the prophylactic 

 against pest recommended by Terni and Bandi. The two methods 

 are practically identical as Bandi 51 has recently pointed out. However, 

 it must be admitted that Bandi did not originally explain the principle 

 of the action of his prophylactic, as we understand its action to-day after 

 a study of the subjects of free receptors and of aggressins. The method 

 of inoculation with natural plague aggressin is not likely to come into 

 general use because of the great difficulties encountered in the prepara- 

 tion of the prophylactic. Moreover, in my experiments I have not 

 obtained the satisfactory results with it which Hueppe and Kikuchi 

 evidently anticipated. The method of vaccination, as already mentioned, 

 gives a much greater degree of protection. Although Klein's method, 

 according to the small number of experiments I have performed, gives 

 about the same results in immunizing guinea pigs as are obtained by the 

 inoculations with natural aggressin, yet the injection of the former 

 substance as prepared in my experiments produced a much greater local 

 reaction than the latter. Therefore, I could not ascertain that this 

 method had any particular advantage over that in which inoculations of 

 natural aggressin were employed. 



I performed no experiments with Lustig's plague prophylactic, partly 

 because of the poor results which Kolle and Otto 52 encountered in their 

 experiments and partly because the results which have been obtained 

 in this laboratory by the use of this method in extracting the immunizing 

 substances from the cholera spirillum have not been encouraging for its 

 further use; other methods of extraction of these substances from the 

 bacilli having in my opinion given more satisfactory results. 



"■"Deutsche Med. Wchnschr. (1905), 31, 1101. 



sl GmtrU. f. Bakteriol. (1906), 42, 448. 



52 Ztschr. f. Hyg. u. Infectionskrcmkh., Leipz. (1903), 45, 517. 



