METHODS FOR THE MICROSCOPIC STUDY OF BACTERIA 205 



V. The Cultivation of Bacteria. Inoculation of Culture Media. 



A platinum wire of 24-gauge is generally used to transfer bacteria from 

 medium to medium. A piece of platinum wire 1 three inches in length 

 is fused into the end of a glass rod 5 mm. in diameter and about 15 

 cm. in length. Metal handles are preferred by many; they possess 

 the great advantage of not breaking, but become heated during the 

 process of sterilization. The straight wire or "needle" is commonly 

 used for the inoculation of slant and stab cultures in solid media; 

 for the inoculation of fluid media a loop is formed on the end of the 

 wire. The use of the loop permits of the transfer of a greater amount 



FIG. 23. Needle sterilizer. (A. de Khotinsky.) 



of material. It is occasionally necessary to transfer more material 

 than a drop or two obtained with a loop in order to insure growth, 

 and for this purpose sterile capillary pipettes are very convenient. 

 Many anerobic bacteria and organisms which grow poorly in artificial 

 media must be transferred with the pipette. 



The transfer of bacteria from media to media involves the following 

 steps : 



(a) Flame cotton plugs to destroy molds and spores of bacteria; 

 extinguish flame. 



(6) Twist cotton plugs to destroy adhesion to the neck of the 

 tube. The plugs may then be removed intact. 



(c) Sterilize platinum wire in Bunsen flame. Heat wire white hot 

 and pass that portion of the handle adjoining the wire through the 

 flame, rotating it between the fingers while doing so. Allow the wire 

 to cool. 



(d) Grasp the tubes in the left hand and remove plugs from the 

 tubes, holding one between the third and fourth fingers of the right 



1 A cheap and efficient substitute for platinum wire is "Nichrome" wire. It is rather 

 less durable than platinum, and melts at a lower temperature. 



