BACILLI OF THE COLON. 
67 
All blood contains a small amount of agglutinating 
substance; so the serum is diluted, say, to 1:40 or 
1: 80 and mixed with a fresh bouillon culture of ty¬ 
phoid bacilli in equal parts. The mixture is now under 
the microscope, and if the agglutinins are present the 
typhoid bacilli will be seen drawn together into clumps 
or clusters and lose their motility. When clumping is 
complete the reaction is said to be positive, and means 
that the patient now has or recently has had typhoid 
fever. Negative reactions are of no significance, as 
the reaction is not constant, being present one day and 
absent the next. A positive reaction, however, is con¬ 
clusive. 
