8o CLINICAL BACTERIOLOGY AND HyEMATOLOGY 



sedimentation-tubes containing a definite bulk of killed typhoid 

 emulsion and sealed at each end ; each tube also contains a small 

 amount of mercury. Accompanying each of these tubes there is 

 a short length of capillary tubing (about i inch long) ; this will 

 hold a definite fraction (|, ^^, ^^i etc., according to requirements) 

 of the amount of emulsion in the sealed tubes. To use them, 

 collect the blood in the ordinary way in a Wright's blood capsule, 

 pipette, etc., and let it coagulate. It is necessary to get clear 

 serum for the test, but it is usually quite easy to do this, even 



Fig. 25. — Positive and Negative Widal's Reaction : Macroscopic 



Method. 



The fluid in the left-hand pipette (negative) is still turbid. The right-hand 

 pipette (positive) contains clear fluid, and has a sediment at the bottom. 

 The lower portions of the pipette have been removed. 



without a centrifuge. File and break the pipette so that the 

 serum is exposed ; then take the capillary tube and touch the 

 surface of the serum, which will ascend the tube and just fill it. 

 File and break off the tip of the sedimentation-tube (at b, Fig. 26), 

 drop in the capillary tube full of serum, reseal the tip of the tube, 

 and allow it to cool. When cold, shake it violently for half a 

 minute (when the mercury will act as a stirrer), and put it to 

 stand in a vertical position. The whole process takes about two 

 minutes, and is about as easy as testing for albumin. In positive 

 cases the first indication of a reaction may be seen in about an 

 hour, and it is usually complete in four or five. The fluid first 



