THE MICROSCOPE IN MEDICINE AND SANITATION. 119 
foreign cells; sometimes they cause them to clump to- 
gether in masses and to settle out of the fluid in which 
they are suspended. In the blood of an individual in- 
fected with typhoid fever, bodies of the last type, known. 
as agglutinins, are present; and their clumping reaction is 
specific for that particular micro-organism. It is true that 
the blood of a normal individual may contain substances 
which agglutinate typhoid bacilli, but that of a typhoid 
patient has the power to such a high degree that it will 
produce the same effect much more rapidly and in high 
dilution. In making the diagnosis of a suspected typhoid 
case, a sample of blood is taken from the lobe of the ear 
in the usual manner and allowed to clot in a small test- 
tube so that the corpuscles are separated from the clear 
straw-colored serum. A drop of serum is then mixed 
on a slide with 40 drops of a fresh broth culture of the 
typhoid bacillus. The mixture is covered and examined 
under the 7y-inch oil-immersion objective. At first the 
bacilli may be seen, after careful focussing, as minute trans- 
parent rods, singly, or in pairs and short chains, moving 
rapidly about across the field of the microscope. If agglu- 
tinins be present, the bacteria become motionless and clump 
together in masses, sometimes large enough to be visible 
to the naked eye. If the reaction is not obtained with 
a 7p dilution, another drop of serum may be added, and 
if this fails, again, another. The latter dilution, ;'5, should 
clump the bacilli in fifteen minutes if the case examined 
be typhoid fever; with a 7p dilution an hour’s time may 
be needed. The test may be made quite as well with dried 
blood after diluting with the proper amount of water. 
