BACILLI OF THE COLON. 



63 



and is liberated only after death and disintegration of 

 the organisms. An active immunity to the disease 

 can be produced by injecting the killed typhoid bacilli, 

 which after disintegration set free their poisons in the 

 blood and stimulate the organs and tissues of the body 

 to form protective substances that prevent infection. 

 This method of creating immunity to typhoid has been 



c. D. 



Fig. 7. Stages of the Widal reaction. (After Robin.) 



practised a great deal in the last two years with very 

 gratifying results. It was first tried in this country in 

 the U. S. Army maneuver camp at San Antonio, 

 Texas; 8097 men were vaccinated, that is, they were 

 injected with a killed culture of typhoid bacilli on 

 three occasions, the dose being increased each time. 

 Only one case developed among these men, and this 

 one was not fatal. 



Among nurses and hospital attendants the anti- 



