32 VACCINE AND SERUM THERAPY. 



a rubber teat which is attached to the large end of the pipette, 

 leucocytic cream is drawn into the capillary end up to the mark. 

 Then the capillary end is withdrawn from the leucocytic emulsion 

 and the emulsion in the tube is drawn about one quarter inch 

 further up into the tube. After this the capillary end of the 

 pipette is immersed in the bacterial emulsion, which is taken into 

 the tube up to the mark. The tube is withdrawn and again a 

 small amount of air drawn into the capillary tube. After this the 

 serum is drawn in, again taking the amount necessary to fill the 

 capillary pipette to the mark. Walker has suggested that small 

 quantities of serum and leucocytic cream be put into small tubes 

 and that serum and leucocytes be taken only once from each of 

 these small tubes. This is done in order to avoid carrying ma- 

 terials from one tube into another. 



The capillary pipette now contains equal volumes of leuco- 

 cytic cream, bacterial emulsion, and serum, as is shown in Fig. 9. 



FIG. 9. 



All three volumes are now forced out onto a glass slide, being drawn 

 in and out with the pipette in order to mix the three parts thor- 

 oughly. When this has been done the mixture is drawn into the 

 tube and allowed to come about half way up the capillary/part 

 when the open end is sealed off infa* pilot flame of the^Bunsen 

 burner. Walker mixes the three factors in -a small test j tube 

 taking precautions against air bubbles. Slides, however, have 

 seemed better adapted especially because air bubbles are more 

 easily avoided. 



After sealing the capillary pipette, containing the mixture of 

 leucocytes, bacteria and serum, it is incubated at 37 C. Realiz- 

 ing that the pipette containing the mixture will not assume the 

 temperature of the thermostat if it is merely exposed to the air 

 in the thermostat, Wright originated a so-called opsonizer. 



The length of time for which the mixture is incubated varies 

 for the different organisms. It is to be noted that up to a certain 



