THE STUDY OF THE GROWTH OF BACTERIA IOQ 



To isolate a pure culture of bacteria, say the Bacillus pyocyaneus 

 from pus, the following procedure is adopted in this method. 



Three sterilized petri dishes, and three tubes of gelatine melted 

 at 40 C. are used. A loopful of pus is taken up by a sterilized 

 platinum loop and mixed with the gelatine of the first tube. To do 

 this the tube is held across the left hand in a horizontal position and 

 the cotton plug is removed, and held by its outside end between the 

 fingers of the left hand, care being taken to prevent the tubal part 

 of the plug touching anything and being contaminated. The plati- 

 num loop is then slowly and carefully introduced into the medium, 

 and stirred around so that the tube walls are not touched. The 

 needle is again sterilized and tube number two is held in the palm 



FIG. 32. Method of inoculating culture media. (Williams.) 



of the left hand parallel to the first one and its plug is removed also ; 

 then with a carefully sterilized needle, three loops of the inoculated 

 gelatine are removed from number one and mixed with number 

 two tube. The needle is then again carefully sterilized in the flame, 

 the plug of number one is carefully replaced and another tube, 

 number three, is held in the palm of the left hand and its plug is 

 carefully removed and held as the previous ones were. With the 

 sterilized loop three loopfuls of the gelatine from number two are 

 carefully introduced into number three and the needle is then steril- 

 ized and put aside. The petri dishes should now be laid on a 

 cold level slab, and the contents of the tubes run into the differ- 

 ent dishes. Tube number one is taken first; the lip of the tube is 



