112 THE ACUTE SELF-LIMITED INFECTIONS 



of fact, it can be shown by laboratory methods that blood 

 after typhoid fever has more power to destroy the bacilli 

 than before the attack; that is, it has more bacteriolysin than 

 is possessed by the blood of a person who has never suffered 

 from typhoid. 



Widal Test. Far more important antibodies are the 

 agglutinins used extensively in the diagnosis of the disease. 

 These are bodies in the blood which when brought into 

 contact with the bacilli, make them stop moving and clump 

 together. To use this for diagnostic purposes a fluid culture 



FIG. 35. Microscopic field, showing the top of a drop with the typhoid 

 reaction. (Park.) 



or salt solution suspension of the living, actively motile 

 germ is prepared. Some blood from the patient is obtained, 

 the clear serum collected and mixed with the bacterial sus- 

 pension in dilution of 1 part of the serum to 20, 50, 100 or 

 more parts of the bacterial suspension. These dilutions are 

 used because sera from some persons entirely free from 

 typhoid will clump the bacilli in low dilution, 1 to 5 or 1 to 

 10. The mixture of serum and bacteria is observed under 

 the microscope after they have stood together for a definite 

 time, and the presence of clumping, with loss of movement, 



