60 GENERAL MICROBIOLOGY 



5. Transfer to one of the agar slants, making a streak 

 along the median line of the inclined surface of the agar, 

 drawing the needle from the base to the top of the slant. 



Note. For investigational purposes, when dealing with unknown 

 microorganisms, the following method is more accurate for obtaining 

 them in pure culture: Transfer to a tube of broth; incubate for 

 twenty-four hours and plate a second time. Isolate from the twenty- 

 four-hour plate culture. 



6. Incubate at the optimum temperature. 



Note. If the agar slants haye become dried out to any extent, it 

 is necessary that the agar be melted and re-slanted in order that 

 optimum growth may take place. 



EXERCISE 16. METHOD OF MAKING TRANSFERS OF 

 PURE CULTURES INTO A LIQUID MEDIUM 



Directions for making transfers of pure cultures from 

 one medium to another must be followed very carefully, 

 otherwise extraneous microorganisms may enter and hope- 

 less confusion result. 



Apparatus. Test tubes containing a sterile liquid 

 nutrient medium; platinum needle; Bunsen burner. 



Culture. Pure culture. 



Method. 1. Flame the cotton plugs of the test tubes 

 containing the pure culture and the sterile liquid nutrient 

 medium. 



2. Sterilize the platinum needle in the flame. 



3. Permit it to cool (about one minute is required). 



4. Hold it in the right hand and remove the cotton plug 

 of the culture tube with the little finger of the same hand. 



5. Take up a very little of the culture with the needle. 



6. Replace the plug of the culture tube. 



7. Remove the plug of the tube of sterile liquid medium 

 in the same manner. 



8. Insert the infected needle into the liquid. 



9. Replace the plug. 



10. Sterilize the needle before laying it down. 



