THE AGGLUTINATION REACTION 



283 



(a) First inspect the control. The bacilli should not be clumped, 

 but should be motile, and preferably in the form of long slender rods. 

 (See Fig. 78.) 



(6) Examine the 1 : 40 and 1 : 80 dilution preparations: a positive 

 reaction is indicated by loss of motility and definite clumping (Fig. 80). 

 A few free motile bacilli may be seen, or a clump may be seen to move, 

 owing to the efforts of the bacilli to break away. A doubtful reaction 

 is indicated by a partial loss of motility and a few indefinite clumps. 

 A negative reaction is indicated when there is no loss in motility or no 

 clumping, or when the reactions resemble the control to which no serum 

 has been added. In reporting 

 upon agglutination tests always 

 state the time at which the test 

 was made and the dilution used. , 



A 1 : 20 and a 1 : 40 dilution 

 may be prepared and examined at 

 the end of half an hour. Prompt 

 agglutination is found practically 

 only in typhoid fever. 



Dilutions may be conveniently 

 prepared by drawing the serum up 

 to the mark 0.5 in the white cor- 

 puscle pipet, and the distilled water 

 up to the mark 11. Mix well. 

 This gives a dilution of 1 : 20. 

 One loopful of this diluted serum 

 and one loopful of bouillon culture 

 of the microorganism to be tested 



give a dilution of 1 : 40. One loopful of the 1 : 20 diluted serum and 

 three loopfuls of the culture give a dilution of 1 : 80. Having mixed the 

 diluted serum and the bacterial suspension on a cover-glass, prepare the 

 cultures on the vaselined concave slides in the usual manner. 



FIG. 80. A POSITIVE AGGLUTINATION 

 (WIDAL) REACTION IN TYPHOID FE- 

 VER. X 430. 



Serum from a patient ill about 



twenty-two days; a 1 : 100 dilution at 



the end of one hour. 



THE MICROSCOPIC AGGLUTINATION TEST (DRY METHOD) 



(1) Place a loopful of a twenty-four-hour bouillon culture of Bacillus 

 typhosus in the center of a clean cover-glass. 



(2) Moisten the dried blood which has been collected on aluminum 

 foil, glass slide, or paper with a loopful of normal salt solution. (A 

 second and smaller loop may be used for this purpose.) Gently rub up 

 the dried blood and transfer a sufficient amount to the drop of culture 



