66 



PHARMACEUTICAL BACTERIOLOGY 



3. Filling Test-tubes with Culture Media 



The rule is to pour the culture media hot, although this is not abso- 

 lutely essential. For example, if the media are Uquid in the cool or cold 

 state, as bouillon, serum, milk, etc., they may be poured cold. A good 

 rule is to pour a desired amount of the media just as soon as they are 

 prepared, whether they are still hot or merely warm or cold. Of course, 

 gelatin and agar media must be poured hot or must be liquefied before 

 they can be poured. 



Fill a small to medium-sized beaker about two-thirds full of the culture 

 medium. Grasp a plugged tube near the upper end, holding it between 

 thumb and first two fingers of the left hand. Remove the cotton plug by 



Fig. 15.' 



-Diagrammatic sectional view of Arnold steam sterilizer illustrating the prin- 

 ciple of steam formation, circulation and condensation. 



means of the first and second, second and third, or third and fourt^ fingers 

 of the right hand, grasping the free portion of the plug with the back of the 

 fingers toward the cotton. Holding the tube slightly inclined on a level 

 with the mouth, take beaker with medium in right hand (at the same time 

 holding the cotton plug as described), see that the beak rests lightly upon 

 and projects sUghtly over the edge of the tube, and pour, at the same time 

 shifting the eyes to the lower end of the tube to watch the filling process. 

 Fill tubes one-third full. Set down the beaker and replace the cotton 

 plug. Place the filled tubes in special wicker baskets, with a little cotton 

 at the bottom to prevent breaking. Some practice is necessary in order to 

 pour so that none of the liquid comes in contact with the upper third of the 

 tube. This must be avoided, in order to prevent the cotton plug from 

 sticking. Tubes may also be filled from funnel with rubber hose, stop- 



