BACILLUS TYPHOSUS.. 421 
power dry lens (about 1/8 inch) being used, or, some- 
what less serviceably, a 1/12 oil-immersion lens. 
Tue Reaction. If the reaction takes place rapidly 
the first glance through the microscope reveals the com- 
pleted reaction, all the bacilli being in loose clumps 
and nearly or altogether motionless (Fig. 53). Be- 
FIG, 53. 
Widal reaction. Bacilli gathered into one large and two small clumps, the 
few isolated bacteria being motionless or almost so. 
tween the clumps are clear spaces containing few or no — 
isolated bacilli. If the reaction is a little less complete 
a few bacilli may be found moving slowly between the 
clumps in an aimless way, while others attached to the 
clumps by one end are apparently trying to pull away, 
much as a fly caught on fly-paper struggles for freedom. 
If the agglutinating substances are still less abundant 
the reaction may be watched through the whole course 
of its development. Immediately after mixing the blood 
and culture together it will be noticed that the bacilli 
