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 



FIG. 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 



