50 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 indicates de- 

 cidely aerobic tendencies. (Most bacteria are decidedly aerobic; that is, 

 they require 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 cultures is to enable 

 the student to get practice in this preliminary work, particularly as to 

 making the cultural observations above indicated. 



FIG. 33. Kitasato filter for filtering hypodermic solutions, culture media, sera, water, 

 etc. The material to be filtered is placed in the globose container and forced through the 

 clay (infusorial earth) tube (Berkefeld filter bougie) by connecting the receiver with a 

 vacuum pump. All parts of the filter must, of course, be sterilized by heat before and 

 after using. (Williams.} 



The student should now make transfers (subcultures) from the first tube 

 cultures into second tubes, and note whether or not the characteristics 

 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 generally the case, though 

 it must be borne in mind that one and the same species of microbe may 

 undergo considerable change in extended culturing, as indicated in the 

 changed culture characters. In fact, some of the changes are so extreme as 

 to confuse even the most expert bacteriologists. 



