TYPHOID FEVER 115 



no doubt explains some of the hitherto unexplained 

 sources of infection. Attempts have been made to 

 secure an internal disinfection in these cases to pre- 

 vent further elimination of the bacilli. 



Immunity following an attack of typhoid fever is 

 variable, an occasional second or even third attack 

 having been recorded. 



Persons coming from a pure water supply to a 

 polluted water are very susceptible to typhoid 

 infection ; while persons living permanently in a 

 city having an impure water are almost wholly 

 irmnvme. 



The Widal Test is commonly employed as a means 

 of diagnosis, especially in cases lacking the character- 

 istic chnical symptoms. It was discovered by Widal 

 that if living typhoid bacilli were placed in the dilute 

 blood-serum taken from a person suffering with ty- 

 phoid fever, they would speedily lose their motility 

 and become clumped (agglutinated) in characteristic 

 groups. 



Serum-therapy. — Numbers of attempts have 

 been made to treat typhoid fever by a specific 

 serum, but so far the results have not been successful. 



Vaccination for protection against typhoid infec- 

 tion has been much more successful. The vaccine 

 contains bacterial cells or substances derived from 



