326 Influence of the Constituents of a Bacterial Emulsion, etc. 



bacilli, quite weak suspensions of living typhoid bacilli can be used for the 

 purposes of a differential test. 



The same thing holds, as our experiments have shown, in connection with 

 the opsonic power. If, as in Experiments 4 and 5, we partially deplete our 

 sera of opsonic power by the addition of detritus to the phagocytic mixture, 

 we can use quite weak suspensions of intact bacilli for the purposes of the 

 differential opsonic test, and this will give us a sensitive indicator which will 

 keep the bacterial ingest within the limits which will allow of its being 

 accurately enumerated. 



And we have here also a new and important point. If only a small 

 quantum of detritus is present it will be possible to differentiate subnormal 

 from normal indices, but not supernormal from normal ; and not until we 

 have sufficient detritus can we hope to differentiate both subnormal and 

 supernormal from normal. We can, in short, only obtain a perfect indicator 

 of differences in opsonic power by preparing our emulsions in such a way as 

 to contain this sufficiency. This is clearly brought out in the latter experi- 

 ments of Series V. And further, perhaps the most important result of these 

 experiments is to explain the fact that with one and the same blood very 

 different opsonic indices may be obtained by different workers, and even by 

 the same worker at different times. 



