COLLECTING BACTERIA FROM THE AIR 41 



when removing it from the tube, take care not to touch 

 the walls of the tube. If any cotton accidentally sticks 

 to the mouth of the tube, it should be burnt off with 

 a hot platinum needle, and then the mouth of the tube 

 passed through the flame before inserting the needle. 



6. Insert the needle with the culture into the sterile 

 tube, and carefully draw along the surface of the slant, 

 turning the needle during the operation and without 

 puncturing the jelly. 



7. Sterilize the needle in the flame, as above, and 

 replace the cotton plugs. It is not superfluous to repeat 

 here that the platinum needle should always be flamed 

 immediately after taking it up, and again before laying 

 it down. 



A stab-culture is made in the same manner as a slant- 

 culture, except that the medium is punctured centrally 

 by a quick, steady movement of the needle. Care should 

 be taken not to let the needle touch the bottom of the 

 tube, the object being to make as narrow a puncture as 

 possible, and by touching the glass the needle would bend 

 and make a ragged opening in the medium on with- 

 drawing. 



Inoculations of liquid media are made the same as 

 agar-slants, except that the end of the needle is gently 

 rubbed against the glass below the surface of the liquid. 

 The medium is then shaken. After inoculation milk- 

 cultures should never be shaken again, as this might 

 destroy a characteristic shape of the coagulum or break 

 up the cream-ring. 



Inoculations from liquid media are made with the 

 looped needle. This may also be used, if a considerable 

 amount of growth is required on a solid medium. The 



