62 BACTERIOLOGY. 



are very much increased after typhoid, and by experi- 

 ment it can be shown that the blood of patients after 

 recovering from typhoid has marked power to dis- 

 solve the typhoid organisms. The agglutinins possess 

 the power of drawing the typhoid bacilli into clusters 

 or clumps. This phenomenon is made use of in de- 

 tecting the presence of typhoid fever by what is known 

 widai as the Widal reaction. It is made in this way: A 



reaction 



small amount of blood is drawn into a capillary tube 

 from the patient's ear and allowed to clot. By clotting 

 the serum is separated from the blood. The object 

 of the test is to see if the serum contains any agglu- 

 tinins of typhoid bacilli. All blood contains a small 

 amount of agglutinating substance; so the serum is 

 diluted, say, to i : 50 or i : 100 and mixed with a fresh 

 bouillon; culture of typhoid bacilli in equal parts. The 

 mixture is now watched under the microscope, and if 

 the agglutinins are present the typhoid bacilli will be 

 seen drawn together into clumps or clusters and lose 

 their motility. When clumping is complete the re- 

 action is said to be positive, and means that the pa- 

 tient now has or recently has had typhoid fever. 

 Negative reactions are of no significance, as the 

 reaction is not constant, being present one day and 

 absent the next. A positive reaction, however, is 

 conclusive. 



Quite recently the prevention of typhoid has been 



immunity greatly advanced by what is known as vaccination. As 



V - 



mentioned earlier in the chapter, the poison of the 

 typhoid bacilli is found within the body of the cells, 



