210 ACTIVE IMMUNIZATION 



by exposure to sunlight for twenty-four hours. Some of the mate- 

 rial is then scraped off, ground up in an agar mortar with 1.5 per cent, 

 saline and centrifugalized to remove clumps. Cole states that if con- 

 tamination is guarded against the supernatant fluid may be used for 

 at least a month. I have not had occasion to use emulsions prepared 

 in this manner, and am familiar only with emulsions made from 

 dead and ground-up bacilli. A small quantity of this material 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, of 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 capil- 

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

 of from 0.5 to 1.0 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, 

 above) 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 



