AGGLUTINATION REACTION 233 



In all cases two or three different dilutions should be made to 

 exclude the possibility of a " zone of no reaction " with some parti- 

 cular dilution (see p. 225). 



2. Macroscopic, or sedimentation method. The serum, having 

 been diluted by means of a pipette with saline solution, is mixed 

 with five to twenty times its volume of culture suspension con- 

 taining plenty of micro-organisms in the same manner as described 

 in the previous section. The mixture is sucked up into a fine, 

 but not capillary, bore tube. This is sealed at the lower end and 

 allowed to stand in the upright position for eight to twenty-four 

 hours at 20 C., or six hours at 37 C. ; the reaction is often dis- 

 tinct within an hour at 37 C. When the reaction is positive the 

 organisms become agglutinated and form flocculi, which are easily 

 seen with the naked eye or with a hand-lens and stick to the sides 

 or sink to the bottom of the tube. The dilutions usually employed 

 are 1 in 30 to 1 in 200, and two or three different dilutions should 

 always be put up. Whole blood is not suitable for the sedimen- 

 tation test ; clear serum should always be used. It is well to set 

 up at the same time a control tube with saline solution, or, prefer- 

 ably, with normal serum. 



For the macroscopic test a thickish suspension of an agar cul- 

 ture in saline should be used ; it should be centrifuged for a few 

 minutes, or be allowed to sediment for an hour, before use to 

 remove large masses. 



If sufficient serum is available the mixture may be put up in 

 little test-tubes, such as the inner tubes of Durham's culture 

 tubes (p. 80). 



3. Dreyer's method. The Dreyer " Standard " method is now 

 much used for the diagnosis of typhoid and paratyphoid fevers and 

 bacillary dysentery (see " Typhoid Fever "). 



4. Garrow's method.^ This is an exceedingly handy and rapid 

 method for carrying out agglutination tests in supposed cases of 

 typhoid and paratyphoid fevers and bacillary dysentery ; it may 

 also be employed in other infections and also for the Bordet- 

 Durham reaction for the identification of organisms. Thick 

 emulsions of the required organisms are prepared by emulsifying 

 young agar cultures in saline containing 0-1 per cent, of formalin. 



1 Journ. Roy. Army Med. Corps, May, 1917. 



