Laboratory Outline for General Bacteriology 



CAUTIONS AND DIRECTIONS FOR IDENTIFICATION 

 OF UNKNOWN CULTURES 



1. Don't allow cultures to become contaminated. Later work 

 with contaminated cultures gives incorrect results. The fol- 

 lowing notes give some hints about avoiding contaminations 

 and obtaining satisfactory records. 



Agar Slants 



2. Don't lay cotton plug on the table or let it fall there, or hold 

 the inner part of the plug next the palm of the hand, or 

 allow it to touch anything. If it accidentally touches anything 

 burn off a layer of the cotton before replacing plug in tube. 



3. Don't pull off cotton adhering to the mouth of the tube with 

 the fingers, rods, matches, etc. Burn it off. 



4. Don't use the needle or loop without first thoroughly steriliz- 

 ing it by heating the entire length to redness and passing the 

 lower part of the holder three or four times through the flame. 



5. Don't use the needle or loop when hot enough to kill the 

 bacteria. 



6. Don't feel of the needle with the fingers or touch it against 

 something not sterile to see if it is cool enough to use. 



7. Don't open tubes in currents of air. Bacteria are blown in. 



8. Don't hold tubes vertical when open thus allowing bacteria 

 to fall in. 



9. Don't insert plugs so slightly that they fall out when tubes 

 are handled. 



10. Don't be careless with cultures when you think it may be the 

 last time you are going to use them. You frequently find 

 they are needed for later work. 



11. Don't discard any cultures until you are advised to do so. 



12. Don't make partial records of cultures when complete ones 

 are possible. 



13. Don't leave record spaces blank when you find that no change 

 has taken place or when you obtain a negative reaction. 



14. Don't record the color of the medium under "chromogenesis" 

 or leave the space blank if the bacterial growth is white or 

 colorless. 



15. Don't break the surface of the agar slant with the needle or 

 loop. The bacteria are usually entirely on the surface of the 

 agar and mixing them with the agar greatly increases the 

 difficulty of making later inoculations. (Continued on Page 25) 



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