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PHARMACEUTICAL BACTERIOLOGY 



h. Deep stab culture where is growth most active? If at bottom, 

 it indicates anaerobic tendencies. If limited to top of medium, it indi- 

 cates decidedly aerobic tendencies. (Most bacteria are decidedly aerobic; 

 that is, they require free oxygen to thrive.) 



The test-tube cultures do not necessarily represent pure cultures, 

 and the student cannot know whether the growths in the test-tubes 

 represent the predominating bacterial flora in the substance from which 

 the inoculations were made. The chief object in making the above 



FIG. 34. Streak culture on agar in a Petri dish. (Delafield and Prudden.) 



cultures is to enable the student to get practice in this preliminary work, 

 particularly as to making the cultural observations above indicated. 



The student should now make transfers (sub-cultures) from the first 

 tube cultures into second tubes, and note whether or not the charac- 

 teristics originally noted are continued or repeated. If the transfer 

 cultures are the same as the originals, it is an indication that the first 

 cultures were pure (representing one species or variety), which is gen- 

 erally the case, though it must be borne in mind that one and the same 



