326 INFECTION AND IMMUNITY. 



Bacteria. The bacteria are obtained by growing 

 on the surface of an agar slant for from 12 to 24 

 hours; they are then removed into salt solution 

 either by means of a loop or by adding the salt 

 solution directly to the agar slant. The concen- 

 tration should be such that a smear on a slide 

 shows plenty of bacteria to the field of the micro- 

 scope while at the same time the individual organ- 

 isms are well separated from one another. Fre- 

 quently to obtain such a mixture it is necessary 

 to shake the emulsion thoroughly to insure divi- 

 sion of clumps. 



Having the above constituents they are mixed 

 together in the following way: 



A capillary tube is made by drawing out a glass 

 tube of about 4 mm. caliber and a length of about 

 16 cm. A small volume of serum is allowed to 

 run into the tube by capillary attraction and the 

 length of the volume marked on the outside of 

 the tube. A small air bubble about 1 mm. in 

 length is then drawn into the tube and then a vol- 

 ume of bacterial suspension equal to the volume 

 of serum. Again a small bubble of air is drawn 

 into the tube and lastly a volume of leucocyte mix- 

 ture equal to those of serum and bacteria. 



The three constituents are then mixed together 

 by drawing the three up into the large part of 

 the tube and mixing together there by drawing 

 back and forth or they may be mixed on a glass 

 slide and then drawn back into the capillary tube. 

 The mixture is then incubated the desired length 

 of time (usually about 15 minutes) and smeared 

 on a slide as in making an ordinary blood smear. 



