206 PHAGOCYTOSIS. OPSONINS AND BACTERIOTROPINS 



quired 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 emulsion is made. For use, a small portion of the resultant emul- 

 sion is centrifugalized until 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 



FIG. 25. 



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. 



Streptococci may similarly be rubbed up in a mortar with 0.85 per 

 cent, salt solution and then centrifugalized. As a rule, however, vigorous 

 pipetting into a watch glass with subsequent centrifugalization for a few 

 minutes is sufficient to break up the chains and leave a satisfactory 

 emulsion. 



If several specimens of blood are to be examined it is best to do a 

 preliminary phagocytic count in order to test the strength and condition 

 as regards clumping of the emulsion. The phagocytic count for tubercle 

 should be between 1.5 to 2 per cell and for other organisms not less than 

 3 per cell. According to the preliminary finding further dilution or 

 concentration of the emulsion is necessitated. The pipe tes employed 

 for the opsonic index should b about 16 cm. long and made from glass 

 tubing about 5/16 of an inch in diameter. They should all be approxi- 



