THE AGGLUTINATION REACTION 287 



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

 placed in the incubator at 37 C. for two hours. The tubes are then 

 allowed to remain at room temperature for six hours, or in the re- 

 frigerator 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 



FIG. 84. AGGLUTINOSCOPE (Altman). 



The test-tubes are arranged in the rack and viewed from below in the mirror. 

 In this manner the smallest deposits are easily seen and compared with the control. 



broken up by gentle agitation. A positive reaction shows masses and 

 clumps of bacteria adhering to the sides and bottom of the tube, which 

 are broken up with some difficulty (Fig. 82). The supernatant fluid 

 should be clear. As dilutions become higher and the amount of con- 

 tained agglutinin correspondingly less, agglutination becomes less and 

 less complete. There is less sediment, and the turbidity of the super- 

 natant fluid is greater, until the negative tube closely resembles the cul- 



