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 i;V-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 5V dilution, another drop of serum may be added, and 

 if this fails, again, another. The latter dilution, iVi should 

 clump the bacilli in fifteen minutes if the case examined 

 be typhoid fever; with a 4V 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. 



