RESEARCHES ON CERTAIN PROBLEMS OF PLAGUE IMMUNITY 35 



act by combining with the lysin of the serum, and thus interfere with the 

 bacteriolytic process. 



Such artificial aggressins must be regarded as closely related to 

 certain bacterial toxins. One need only recall here, that the method 

 employed by Wassermann and Citron is practically identical with 

 Besredka's method for obtaining plague toxin. 



The powerful immunising action of the natural aggressins, compared 

 with the weak immunising action of these artificial aggressins, is used by 

 Bail as an argument in favour of the essential difference in the nature of 

 the two groups of bodies. 



It is impossible here to enter into a full discussion of the relation 

 of the aggressins to the " free receptors" of Neisser and Shiga (1903), and 

 to the substance, demonstrated by Pfeiffer and Fried berger (1905), in 

 serum, after its treatment with emulsions of typhoid and cholera 

 organisms. 



The intimate relation which these subjects bear to plague immunity is 

 emphasised by certain work carried out in the Laboratory here, by 

 Captain Douglas, I. M.S. (1906), recorded in a paper read at the 

 Pathological Society of London, in which he showed that, contrary 

 to the view taken by the German and English Plague Commissions, 

 the supernatant fluid of Haffkine's Prophylactic Fluid has powerful 

 immunising properties, as had been previously maintained by Haffkine. 

 Where the prophylactic fluid was prepared by emulsifying the bacillus 

 from agar in normal salt solution, the supernatant fluid, in this case also, 

 was demonstrated to possess an immunising property. The writer 

 has shown that the injection of the supernatant fluid in the horse gives 

 rise to the production of a small amount of antitoxin. It is difficult 

 to reconcile with these results of Douglas the statement made by Bail 

 and Weil (1906), that attempts to immunise with watery extracts against 

 the true parasites prove absolutely futile, since the B. pestis has been 

 classified by them in this group. 



Neisser and Shiga in the case of the dysentery bacillus of Shiga and 

 the typhoid bacillus, obtained analogous results which they attributed to 

 the presence of free receptors in the filtrates from the autolysed bacilli. 

 In that case bacteriolytic sera were obtained ; in the case of plague we 

 have shown that no matter whether the two fluids employed by Douglas 

 and the writer or the living bacillus are used in the treatment of the 



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