TYPHOID FEVER 8l 



shows a slight granularity, which becomes more and more marked, 

 minute greyish flocculi separating themselves from the uniformly 

 turbid emulsion. These flocculi gradually get bigger and settle 

 slowly at the bottom of the tube, leaving the supernatant fluid 

 almost clear. The emulsion will settle by itself, but very slowly, 

 and falls as a powdery deposit quite different from the flocculi. 

 An unused sedimentation-tube (shaken immediately before use) is 

 put side by side with the one containing the serum, and used as a 

 control ; the two are inspected from time to time, and if there is 



Fio. 26. 



3, Tube containing emulsion of dead typhoid bacilli and globule of mercury ; 

 b, showing method of inserting the serum in a short length of capillary 

 tubing ; c, a positive reaction ; d, the control. 



no obvious difference in five or six hours the reaction is absent. 

 The presence of the reaction in a dilution of i in 20 is fairly 

 definite proof of infection. 



The tubes are a little trouble to prepare, but a stock sufficient 

 to last for months may be made at the same time. Prepare 

 the typhoid emulsion in the method already described (p. 72). 

 Next prepare some tubes of the shape shown on Fig. 26, 

 sterilize them by dry heat, and place a globule of mercury in 

 each. Then prepare a couple of Wright's pipettes out of a 



6 



