302 



AGGLUTININS 



serum dilution in each. Tube 1 now contains a serum in a dilution of 

 1:20, acting on the bacteria; tube 2, one of 1:40; tube 3, one of 

 1:80; tube 4, one of 1:160; tube 5, one of 1:320; tube 5, one of 

 1 : 640. Tube 7, as just stated, contains the bacterial emulsion in salt 

 solution and is the culture control, 



In determining the agglutination titer of a highly immune serum, 

 these dilutions may be continued to any degree. 



5. On each tube the final dilution is marked with a wax pencil. 



i 



J 





FIG. 85. MACROSCOPIC AGGLUTINATION REACTION. 



Serum of a person who had received three injections of typhoid vaccine. This 

 drawing was made twenty-four hours after the test was set up. The dilutions are 

 marked on the tubes. 



The tubes are then shaken gently, stoppered with cotton plugs, and 

 placed in the incubator at 37 C. or in a water-bath at 55 C. for two 

 hours. The tubes are then allowed to remain at room temperature for 

 six hours, or in the refrigerator for twenty-four hours, after which 

 readings are made. 



6. The culture control should show a uniform cloudiness, with no 

 sediment or flakes, or at most a very slight precipitate that is readily 



