12 QUATERCENTENARY STUDIES IN PATHOLOGY 



found that 32 lethal doses of the endotoxin are neutralised by 0'2 

 grammes of the serum of an immunised horse. 



Similarly, he found that the serum of horses which had been injected 

 intravenously, either with plague bacilli or with the soluble endotoxin, 

 was capable of neutralising the plague endotoxin. 



The Writer's Experiments on Plague Toxin. 



The writer's experiments on the subject of Plague Toxin were 

 directed chiefly to the study of the influence of certain factors on the 

 toxicity of cultures of diflerent races of the plague bacillus. 



Technique used for obtaining the Toxin. — In certain cases the cultures 

 were well shaken with toluol, the bacilli allowed to sediment, and the 

 bacterial free supernatant fluid examined; but for the most part the 

 filtrates of cultures were investigated. The filtration was carried out by 

 means of a " tandem " filter, i.e.^ the fluid was first passed through a 

 Berkefeld, and afterwards through a Pasteur-Chamberland filter. The 

 more porous Berkefeld filter removes the coarser particles, and this 

 prevents the blocking of the Pasteur-Chamberland candle which, 

 employed in this way, always gave a sterile filtrate. The loss of toxin is 

 perhaps less by this method than if the Pasteur-Chamberland candle 

 alone were employed, because in the latter case the blocking of the pores 

 by the larger particles tends to make a very close filter. In every ca.se 

 it is desirable to test the sterility of the filtrates and centrifugalates. 



Temperature. — The temperature most frequently employed for the 

 growth of the cultures was what is generally accepted as the optimum 

 temperature for the growth of the B. pestis, viz., about 30" C. 



The Medium, — The medium employed was the ordinary bouillon 

 such as is used in the preparation of diphtheria toxin. In most cases it 

 was made neutral or very slightly alkaline to litmus, but, with the object 

 of ascertaining whether toxin formation would be aided by the use of an 

 alkaline broth, in certain cases the broth was prepared as for diphtheria 

 toxin, 7 c.c. per litre of normal caustic soda being added after neutralisa- 

 tion with litmus as the indicator. The results obtained with the filtrates 

 from two flasks of the same broth, in the one case neutral, in the other 

 case alkaline, are shown in Tables 1. and II. In this case, the neutral 

 broth appeared to be the more favourable medium for toxin production. 



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