224 ACTIVE IMMUNIZATION 



is placed in an agate mortar and thoroughly triturated with 1.5 per 

 cent, saline, which is slowly added drop by drop. The resultant 

 emulsion may be freed from coarser clumps by centrifugation, but 

 the smaller ones are practically impossible to remove. I have worked 

 with heated and unheated, with extracted and non-extracted bacilli, 

 with 0.1 and 1.5 per cent, saline, but I have not yet seen an emulsion 

 of tubercle bacilli that was uniform. 



In the case of the tubercle bacillus, Wright recommends that the 

 emulsion should be of such strength that in the actual experiment 

 one or two bacilli only are found on an average in each cell. 



The Experiment Proper. Having prepared the patient's serum, 

 normal control serum, washed corpuscles, and the bacterial emulsion, 

 these "reagents" are placed in a small rack, or in a dishful of sand 

 covered with a piece of white filter paper, perforated to receive the 

 tubes, and marked accordingly. 



Mixing pipettes (Fig. d or e, Plate III) are prepared from glass 

 tubing having an outside diameter of approximately 6 mm. To 

 this end pieces of tubing are cut, measuring about 15 cm. in length, 

 heated in the middle in the flame of a Bunsen burner until soft, 

 and then drawn out after removal from the flame, so that capillary 

 stems are obtained about 10 to 15 cm. long, with a diameter of from 

 0.5 to 1 mm. The ends are cut off square with a fine file. The 

 tubes are marked about 1 to 2 cm. from the ends with a glass pencil 

 and before use provided with medicine-dropper rubber nipples. One 

 volume of the leukocytic "cream" (see Preparation of Leukocytes, 

 p. 222) is then drawn up to the mark, followed by one volume of 

 serum and one of the bacterial emulsion, the three portions being 

 separated from one another by little bubbles of air (see Fig. d, Plate 

 III). The contents of the tube are next blown out upon a slide 

 by gentle pressure upon the rubber nipple, well mixed by drawing 

 them up and down in the capillary tube, then taken up in solid 

 column, and the end sealed in the burner. The tubes are finally 

 incubated for fifteen minutes at body temperature, which may either 

 be done in an ordinary incubator or in a special "opsonifier." 



After incubation the ends of the tubes are pinched off, drops are 

 mounted upon clean slides, and after having been well mixed by 

 passage up and down in the capillary pipette, exactly in the manner 

 in which the mixture was originally made, spreads on slides are 

 prepared by the aid of the narrow edge of a second slide, as in the 



