TECHNIQUE FOR DETERMINATION OF OPSONIC INDEX. 



portion is taken off for use, thoroughly mixed, and if necessary diluted. 

 Emulsions of coliform organisms are more easily made. Frequently it is 

 sufficient to rub up with the platinum loop a loopful of such bacteria on the 

 side of a small test tube containing saline. The proper thickness of the 

 resulting emulsion varies. As a rule, bacillary emulsions are required to 

 have a thicker appearance to the naked eye than coccal 

 ones. The latter should be only slightly opalescent. 



In order to make a satisfactory tubercle emulsion, 

 a more elaborate method is necessary. The dead and 

 dried tubercle bacilli are employed for this purpose. A 

 portion of these bacilli is very thoroughly triturated in 

 an agate mortar, or between two slides, or in a grinder 

 devised for this purpose, at first alone and then with 1.5 

 per cent, salt solution added drop by drop. In this way 

 a paste, and subsequently a comparatively thick emul- 



Leucocytes 

 Air bubble 

 Bacilli 



Mark Air bubble 

 Serum 



FIG. 23, 



FIG. 24. 



sion is made. For use, a small portion of the resultant emulsion is centri- 

 fugalized until only the upper layers are fairly opalescent. 



These upper layers are pipetted off, and thoroughly mixed. A smear of 

 this should be made and stained in order to observe that the emulsion is free 

 from clumps and not too thick. Such an emulsion sealed up in a glass tube 

 and sterilized at 60 C. for i hour can be kept for about one week. 



