TECHNIC FOR PREPARING BACTERIAL VACCINES 209 



way as to bring the microorganisms into suspension. If the culture is 

 not easily washed from the medium, a sterile platinum loop may be used 

 to remove the growth, care being taken not to cut into the medium and 

 mix the fragments with the bacterial suspension (Fig. 57). 



The bacterial suspension thus obtained is poured on the surface of 

 the second culture, bringing this into suspension, and repeating the 

 process until the whole series of cultures have been suspended, adding 

 more salt solution if necessary. 



The final suspension is transferred to a sterile, thick-walled flask 

 containing glass beads, and shaken by hand or in a mechanical shaker 

 until the bacterial masses are broken up (Fig. 58). This may be es- 

 pecially difficult with diphtheria bacilli and streptococci. Unless the 



FIG. 58. A SHAKING APPARATUS (Electric, 110 volts, direct). 



A satisfactory machine for shaking vaccines, preparing antigens, making emulsions, 



etc. 



emulsion is perfectly homogeneous, the larger particles may be removed 

 by brief centrifugalization or, better, by filtering through a sterile filter. 

 There is evidence to show that bacteria grown on culture-media con- 

 taining peptone may produce objectionable toxic substances capable 

 of producing anaphylactic phenomena (Reichel and Harkins 1 ). In addi- 

 tion, when, in the preparation of a vaccine, bacteria grown on a serum 

 medium are washed off with normal salt solution, a portion of the serum 

 may be removed and this may be capable of producing disagreeable 

 local and general reactions. For these reasons it is advisable to wash all 

 suspensions by repeated centrifugalization until the supernatant fluid 

 reacts negatively to the biuret or ninhydrin reaction (Willard Stone). 



1 Centralb. f. Bakteriolog., etc., 1913, 69. 

 14 



