4 QUATERCENTENARY STUDIES IN PATHOLOGY 



the prolongation of the process. On the other hand, considerable risks 

 of thrombosis, causing sudden death, are attached to the intravenous 

 injection of killed cultures. This danger appears to be much greater 

 with killed than with living cultures, and is probably due to the setting 

 free by the heating to which the culture is subjected of a ferment or of 

 nucleo-protein. 



The further stage in the process of immunisation consists in giving 

 the animal a series of intravenous injections of living virulent bacilli. 

 The general experience has been that the injection of even a small 

 quantity of living culture greatly increases the protective action of the 

 serum. 



Roux and Dujardin-Beaumetz at the Pasteur Institute Paris, and 

 Calmette at the Lille Institute, prefer intravenous injections throughout, 

 and use bacterial emulsions, prepared from agar cultures, for both the 

 early and later stages, whereas Tavel Krumbein and Glucksmann at 

 Berne use old broth cultures, killed by heating to 65-70° C. (Hafifkine's 

 Prophylactic Fluid), injected subcutaneously or intramuscularly in the 

 early stages, and young broth cultures injected intravenously in the later 

 stages of immunisation. 



When " anti-plague serum " is referred to in this paper, a serum 

 prepared by one or other of these methods is indicated. In certain of 

 the following experiments the serum used was from animals which had 

 been treated with heated or unheated filtrates only. 



Brief Review of the Literature on Plague Toxin. 



Yersin, Calmette and Borrel (1895) stated that the filtrates from broth 

 cultures of the B. pestis have no toxic action on experimental animals, 

 but that emulsions from agar of the bodies of the bacilli, which have been 

 killed by heating to 58° C, cause the death of guinea-pigs and rabbits 

 when injected subcutaneously or intraperitoneally. 



Roux is stated by Metchnikoff (1897) to have obtained very 

 powerful plague toxins by employing an organism, the virulence of 

 which had been elevated by animal passage in collodion sacs. The 

 filtrate from a bouillon culture, precipitated by ammonium sulphate, gave 

 a toxin of which the lethal dose for a mouse was one-fourth of a milli- 

 gramme, for a rabbit four centigrammes. The guinea-pig is the most 



("4) 



