98 BACTERIOLOGICAL DIAGNOSIS. 
the reaction is present or absent, for the fluid will be 
clear if it is positive, turbid if it is negative (fig. 19). The 
dead emulsion presents more difficulties; you have to 
compare the granular deposit which occurs in a positive 
reaction with the more uniform deposit which occurs in 
the control tube. If there is any doubt the best plan is 
Fic. 19.—Positive and negative Widal’s reaction (macroscopic 
method). The fluid in the left hand pipette (negative) is still turbid. 
The right hand pipette (positive) contains clear fluid and has a 
sediment at the bottom. The lower portions of the pipette have 
been removed. 
to break off the tip of the pipette and blow out some of 
the deposit; examine it under the microscope after 
applying a cover-glass. In a positive case the bacilli 
will be seen to be collected into clumps, in a negative 
case they will remain discrete. 
This process is a modification of that described by 
