304 AGGLUTININS 



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. 85). 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- 



FIG. 87. AGGLUTINOSCOPE (Altaian). 



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. 



ture control. A microscopic examination of a deposit will show that 

 the bacilli point in all directions, whereas in a deposit of unagglutinated 

 bacilli they lie horizontally side by side. 



When agglutinoids are present, agglutination is absent or incomplete 

 in the lower dilutions of serum, and complete in the tubes containing the 

 higher dilutions. This is called pro-agglutination (Fig. 86). 



Readings are facilitated by the use of a special instrument known as 



