12 



MELICK 



This process is repeated in rapid succession from twenty to 

 twenty-five times. The contents of the tubes are then centrif- 

 ugalized, and a clear supernatant fluid is obtained with a 

 compact sediment consisting of fragments of the disintegrated 

 bacterial cells. The supernatant fluid is drawn off and re- 

 centrifugalized. Without further treatment the resulting clear 

 solution constitutes the antigen preparation. It is tested for 

 antigenic and anticomplementary properties. The sediment 

 contains the great bulk of anticomplementary substances with 



T/=J BL.E m 



but little antigen and is discarded. For completeness, a pro- 

 tocol of the antigenic and anticomplementary titrations ob- 

 tained in preparing a given antigen from B. paratyphosus B 

 by the above method are given in Table III. The organism 

 "Paratyphosus B no. 12" was grown seventy- two hours in 

 synthetic medium at 37 C. 



This table shows that the antigen preparation when titrated 

 by the complement fixation method displayed a very great 

 antigen content, in fact distinctly greater than did the total 

 suspension; on the other hand, it completely lacked an anti- 



