458 BACTERIOLOGICAL ANALYSES 



2. Place the tube in the water-bath at 42 C. until 

 the contents are liquid. 



3. Liquefy eight tubes of gelatine-agar and place 

 them in the water-bath at 42 C., and cool down to 

 that temperature. 



4. Inoculate the gelatine-agar tubes with the fol- 

 lowing quantities of the sample by the help of a sterile 

 pipette graduated to hundredths of a cubic centimetre 

 viz., 



To tube No. i add i c.c. liquefied butter. 



2 add o . 5 c.c. liquefied butter. 



3 add o . 3 c.c. liquefied butter. 



4 add 0.2 c.c. liquefied butter. 



5 add o . i c.c. liquefied butter. 



6 add 0.05 c.c. liquefied butter. 



7 add 0.03 c.c. liquefied butter. 



8 add 0.02 c.c. liquefied butter. 



9 add o.oi c.c. liquefied butter. 



5. Pour a plate cultivation from each of the gelatine- 

 agar tubes and incubate at 28 C. 



6. " Count" the plates after three days' incubation, 

 and from the figures thus obtained estimate the number 

 of organisms present per cubic centimetre of the sample. 



Qualitative. 



Apparatus Required: 



Sterile beaker, its mouth plugged with sterile cotton-wool. 



Counterpoise for beaker. 



Scales and weights. 



Sterilised spatula. 



Water-bath regulated at 42 C. 



Separatory funnel, 250 c.c. capacity, its delivery tube protected 

 against contamination by passing it through a cotton-wool 

 plug into the interior of a small Erlenmeyer flask which serves 

 to support the funnel. This piece of apparatus is sterilised 

 en masse in the hot-air oven. 



Large centrifugal machine. 



Sterile tubes (for the centrifuge) closed with solid rubber 

 Stoppers. 



