BACTERIOLOGICAL TECHNIC 



79 



and at a temperature below the coagulating point for albumen, mix thor- 

 oughly; boil for ten minutes, and filter. The coagulating albumen 

 takes up the impurities which remain upon the filter with the albumen, 

 while the medium comes through perfectly clear. 

 Media which have become infected with bacteria as 

 the result of inadequate sterilization should be dis- 

 carded. Do not attempt to clarify them. They may 

 become clear, but they are nevertheless objectionable 

 because of the substances which the bacteria may 

 have liberated and which might interfere with the 

 development of the bacteria to be grown in it 

 subsequently. 



Most of the tubes with solid media (LoeflBer's 

 serum, gelatin, agar, and gelatine-agar) should be burner 

 slants. The slanting surface offers certain advan- 

 tages in making diagnostic bacterial cultures. The 

 usual, non-slanting tubes, for deep stab cultures, 

 should, however, also be held in readiness. Keep all tubes in suitable con- 

 tainers, in a dry, cool, clean place. To guard against infection by mold 

 and other organisms, it is well to cap all tubes with the rubber caps or the 



Pig. 25. — Koch safety- 

 Should the 

 flame be blown out, 

 an automatic devise 

 shuts off the gas. 



Fig. 26. — Hot water funnel with stand and 

 ring gas burner. 



Fig. 27. — Hot water funnel with 

 stand. 



tin foil dipped in corrosive sublimate and paraffin, as already suggested. 

 In case of liquid media, the rubber stoppers or the rubber caps are much 

 preferred, or the hot paraffin may be painted over the tin foil and upper 



