BACTERICIDAL PLATE-CULTURE-METHOD. 



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Topfer and Jaffe pour a thin layer of agar into a petri dish and let it 

 harden. Upon this the culture-serum-agar mixture is poured, and after 

 hardening is covered with another thin layer of agar. In this way the 

 formation of a film of culture in the water of condensation is avoided. 



A practical example is appended to illustrate the plate culture method. 



In addition to the results which one would expect, this experiment shows one striking 

 point. With the normal serum the tube which contains the largest amount of normal 

 bacteriolysins shows on plating, the fewest germs. The greater the dilution of the serum 

 the more prolific is the bacterial growth. The titer of the normal serum in this case lies 

 between i/ioo and 1/500. The controls show that the serum and complement are 

 sterile, and that the inactive normal serum is ineffective. During the three hours in the 

 thermostat the bacterial suspension has become stronger. The retarded growth in 

 the complement culture tube can be traced probably to the presence of normal 

 bacteriolysins. 



With the immune serum on the other hand, results are quite different. Where 

 the most concentrated serum is used, the bacterial growth is still rather profuse; only 

 the moderate doses show a true bactericidal action and the small doses are altogether 

 ineffective. The titer of this serum is between 1/3000 and 1/4000. 

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