RESEARCHES ON CERTAIN PROBLEMS OF PLAGUE IMMUNITY 33 



The experiment shows, therefore, that while there was an apparent 

 inhibition of growth, probably largely due to the agglutinating power of 

 the serum which was i : 300 with a virulent culture, in no single tube had 

 complete destruction of the bacilli taken place, since growth occurred in 

 every one of the tubes containing the serum mixture. 



A number of similar experiments, some of them carried out with the 

 immune horse serum so fresh that the addition of complement was 

 unnecessary, gave perfectly consistent results, e.g., the fresh serum of 

 horse " M B." was tested as above with a bacillus of low virulence, in full 

 strength and in dilutions of i-io, and i-ioo, and i-iooo, and growth 

 took place in all the tubes. 



No matter what method was adopted, it was found impossible to 

 obtain evidence of the serum possessing any bacteriolytic property, even 

 when bacilli of low virulence were used. 



Discussion as to the Nature of the Mechanism by which Anti- 

 Plague Serum Exercises its Anti-Infectious Effect. 



In considering the properties of anti-plague serum we have seen that 

 an antitoxic action can play little part in the protective influence exerted 

 by this serum. It is conceivable that the plague bacillus produces and 

 throws off a large number of toxic particles or receptors under the 

 stimulus of the antagonistic influences which it encounters when intro- 

 duced into the animal body. If this be the case, it seems reasonable to 

 assume that the bacilli, even when grown in artificial media, possess, 

 though in smaller numbers, those toxic particles which are liable to be 

 set free, especially on the death or during the disintegration of the 

 microbes. 



In dealing with the literature of plague toxin reference has been made 

 to several methods of immunisation which are based on the common 

 assumption that certain toxic or immunising substances are produced in 

 a concentrated form in the animal body from which they are recoverable. 

 Thus Terni and Bandi, Hueppe and Kikuchi used peritoneal exudates, 

 and Klein the necrotic areas resulting from plague infection in different 

 organs, as their immunising agent. 



(143) 



