TYPHOID /EVER 89 



Next see that the emulsion is neither too thin nor too thick. 

 No definite rules can be given, but if there are very few bacilli 

 in the field a further supply of growth must be added to the 

 stock of emulsion, and a further specimen examined. If the 

 bacilli are thickly crowded together, the emulsion must be 

 diluted with a little water and re-examined. 



When you are satisfied that the emulsion is right, slide off 

 the cover-glass and drop it into some antiseptic lotion; of 

 course, this is unnecessary if dead cultures are used. 



2. Making the Dilution. You are now about to dilute a 

 drop of the serum from the patient with a known multiple 

 (in this case thirty times) of its bulk of the emulsion which 

 you have just prepared. To do so you will take advantage 

 of the fact that the platinum loop, if dipped into a fluid and 

 pressed against a surface, so that every part of the loop 

 touches that surface, will deposit a drop of fluid of definite 

 size. You are about to mix one loopful of the serum with 

 twenty-nine loopfuls of the emulsion just prepared and 

 examined. 



Blow the blood from the pipette out on to a watch-glass (to 

 do this it will be necessary to break the tip of the pipette), 

 and tilt the latter so that the serum flows away from the 

 coagulum. Now take a loopful of the serum and place it on 

 another watch-glass, taking care to put the loop flat on the 

 surface of the glass; this is done more easily if the wire is 

 slightly bent, or if a flat side is used instead of the watch- 

 glass. 



Next heat the platinum loop in a flame; this is to burn off 

 any blood which might remain on it and contaminate the 

 emulsion. Take up a loopful of the emulsion, and place it on 

 the watch-glass by the side of the drop of serum, but not 

 touching it. Repeat this until you have placed twenty-nine- 

 drops of emulsion round the serum. Mix the whole together 

 by stirring them thoroughly with the platinum loop, place a 

 droplet of the mixture on a clean cover-glass, making a hang- 

 ing-drop specimen, and examine as before. 



If the blood comes from a case of typhoid fever (with cer- 

 tain restrictions which will be discussed below), the micro- 

 scopic appearances will be quite different from those seen in 

 the drop of emulsion which was previously examined. The 

 bacilli will no longer swim about rapidly in all directions ; they 



