CHAPTER VIII 



METHODS USED IN THE CULTIVATION OF BACTERIA 



INOCULATION OF MEDIA 



The transference of bacteria from pathological material to media, 

 or from medium to medium, for purposes of cultivation, is usually ac- 

 complished by means of a platinum wire or loop. The platinum wire 

 used should be thin and yet possess a certain amount of stiffness and be 

 about two to three inches in length. This is fused into the end of a glass 

 rod six to eight inches long. It is an advantage, though not necessary, 

 to use rods of so-called "seaHng-in" glass which, having the same co- 

 efficient of expansion as platinum, does not crack during sterilization. 

 For work with fluid media, the wire should be bent at its free end 

 so as to form a small loop which will pick up a drop of the liquid. For 

 the inoculation of solid media and the making of stab cultures, a straight 

 "needle" or wire should be used. Other shapes of these wires and spat- 

 ulas from heavy wire have been devised for various purposes and are 

 easily improvised as occasion demands. (See Fig. 27.) 



When making a transfer from one test tube to another, the tubes 

 should be held between the thumb and first and second fingers of the 

 left hand, as shown in Fig. 28. The plugs are then removed by grasping 

 them between the small and ring fingers and ring and m.iddle fingers of 

 the right hand, first loosening any possible adhesions between glass and 

 plugs by a slight twisting motion. The platinum wire is held meanwhile 

 by the thumb and index fingers of the right hand in the manner of a pen. 

 The wire is heated red hot in a Bunsen flame, and is then passed into the 

 culture tube without being allowed to touch the glass. It is held sus- 

 pended within the tube for a few seconds to permit of cooling before 

 touching the bacterial growth. The wire is then allowed to touch lightly 

 the surface of the growth and a small amount is picked up. (See Fig. 

 29.) It is then removed from the tube without allowing it to touch the 

 sides of the glass, and is passed into the tube which is to be inoculated. 

 If the tube contains a slanted medium, such as agar, a light stroking 

 motion from the bottom of the slant to its apex will deposit the bacteria 



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