BACILLUS TYPHOSUS 



113 



some antibody formation. Second attacks of typhoid 

 are rare and the reason is probably that a sort of 

 active immunity is gained by one attack. As a matter 

 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. 



FIG. 33 



Microscopic field, showing the top of a hanging drop in a normal typhoid 

 culture. (Park.) 



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 or salt solution sus- 

 pension of the living actively motile germ is prepared. 

 Some blood from the patient is obtained, the clear 

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