96 BACTERIOLOGICAL DIAGNOSIS. 



tube, lay the pipette on its side, and make a mark with 

 ink or with a grease pencil to show how high the serum 

 reaches. Now suck the column of fluid a little way into 

 the tube, and insert the tip of the pipette into the emulsion ; 

 suck the latter up the tube until it reaches to the mark. 

 This will give you the same amount of emulsion as of 

 blood serum ; the two fluids will be separated by a short 

 column of air. Now withdraw the tip for a moment 

 and suck up another small quantity of air ; dip it into 

 the emulsion and suck it up to the mark again. This 

 will give you twice the amount of emulsion as of 

 blood serum, the three portions of fluid being separated 

 by air (fig. 18). Repeat this process until you have 

 nine times the amount of emulsion as of serum ; then 

 suck the fluid still further from the tip of the pipette, 

 and seal the latter in a flame. Probably by this time 

 the fluids will have mixed together ; if not, tap the 

 tube gently (holding it upright) until the air-bubbles 

 which you have sucked up make their escape and the 

 fluid forms a continuous column. 



Fill another tube to a. similar height with emulsion 

 (for a control) and place the two side by side in an 

 upright position for twelve hours. 



Now examine the fluid in the pipettes. If the emul- 

 sion has been made from a living culture the control 

 pipette (i.e., that to which no blood has been added) 

 will probably remain turbid ; if an emulsion of dead 

 bacilli has been used it will have become clear, and the 

 bacilli will form a uniform even layer at the bottom of 

 the pipette. 



Compare the control tube with the pipette to which 

 blood has been added. If the reaction is negative 

 the appearances will be exactly the same in each ; 

 but if the reaction is positive the bacilli will fall to the 



