yS CLINICAL BACTERIOLOGY AND HEMATOLOGY 



with cotton-wool. This serves a double purpose : it prevents any 

 of the fluid from getting into the mouth, and it offers a certain 

 amount of resistance to the escape of the fluid, and thus renders 

 the pipettes more easy to fill. 



Process. — Prepare an emulsion just as before, making a drachm 

 or so, and filtering it. An emulsion of dead bacilli obtained from 

 a laboratory should be ready for immediate use. Insert the tip of 

 the pipette into the blood-serum (of which there should be several 

 drops), and aspirate it gently into the tube, avoiding air- bubbles ; 

 if these gain access, blow out the serum and begin again. It is 

 easier to see what you are doing if you use a piece of indiarubber 

 tubing (such as is used with a haemocytometer) through which to 

 apply suction. 



Having drawn up enough serum to form a column about 2 inches 

 in length in the narrow portion of the 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. 24). 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 emulsion 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. 



