AGGLUTININS 77 



wise unsatisfactory, a bouillon tube can be inoculated 

 from the original agar culture. Before using a cul- 

 ture for the Widal test, the organisms should always 

 be examined for motility. 



(c) Technic of the Widal Reaction. — The micro- 

 scopic test is usually carried out with a depressed 

 hanging-drop slide. The edge of the depression is 

 ringed with vaseline. Upon a clean cover-slip are 

 placed one platinum loopful of the bouillon culture of 

 typhoid bacilli, and one loopful of previously diluted 

 1 in 20 patient's serum, giving a dilution of 1 in 40. 

 The slide is pressed down upon the cover-glass, and 

 quickly inverted so that the hanging-drop remains in 

 the centre of the depression. A similar slide is pre- 

 pared with a dilution of 1 in 80, and a third slide with 

 culture only, to servx as a control for the motility of 

 the typhoid bacilli. Each slide is marked with the 

 dilution and time of beginning the test by means of a 

 grease pencil.^ Each slide in turn is now placed under 

 the microscope, the high-power dry objective (% in.) 

 being used. The typhoid bacilli will be seen to move 

 in all directions through the field. In from % to 1 hour 

 in the case of a positive reaction, all the typhoid bacilli 



* We have found that plain glass slides can be used with equal satis- 

 faction, as reconunended by Stitt. A ring of vaseline is made on the 

 centre of the slide, which is then gently allowed to rest on the cover-glass 

 without any other pressure than its own weight. Sufficient space is thus 

 preserved to allow of motility of the organisms. 



