WIDAL'S METHOD. 91 



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 loop- 

 fuls 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 

 slide is used instead of the watch-glass. 



Next heat the platinum loop in the flame ; this is to 

 burn off any blood which might remain on it and con- 

 taminate the emulsion. Take up a loopful of the emul- 

 sion 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, and make a hanging- 

 drop specimen and examine as before. 



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

 certain restrictions which will be discussed below) the 

 microscopic 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 will become paralysed, 

 and remain quite motionless. Further, they will col- 

 lect into clumps ; each clump consisting of a larger or 

 smaller number of bacilli arranged in a felted net- 

 work resembling that seen in a heap of " spellicans " 



